Tuning the formation and structural polymorphs of FeOOH nanoparticles via iron precursor concentration

The electrolyte gated transistor with a floating gate (FGT) is a promising sensing platform for both chemical and biodetection applications due to its fast, label-free response, low voltage operation, and simple fabrication by printing and conventional lithography. We present here a unified framework for understanding how FGTs measure changes in interfacial capacitance and surface charge, using self-assembled monolayers (SAMs) on the FGT detection area as model systems. The capacitance measurements take advantage of alkyl thiol SAMs with different chain lengths, while the charge experiments deprotonate 11-mercaptoundecanoic acid by changing solution pH. The effects of capacitance and surface charge are identified readily by analysis of the changes in the quasi-static current–voltage (ID–VG) characteristics of a stand-alone FGT in response to changes in the surface properties; changes in capacitance produce changes in slope, whereas changes in surface charge cause horizontal shifts in the transfer curves. For sensing applications, it is preferable to integrate the FGT into a resistor-loaded inverter to take advantage of the amplified voltage output relative to a stand-alone FGT. For inverters, changes in capacitance lead to changes in inverter gain, whereas changes in surface charge produce horizontal shifts in the inverter curves. A capacitance sensitivity of 70 mV/(μF/cm2) and a charge sensitivity of 40 mV/(μC/cm2) are obtained from the inverter output voltages. The ability to sense both capacitance and charge, and to distinguish between them, makes FGTs attractive for the detection of a wide variety of targets in chemical and biological sensing applications.

A novel arginine-based dendritic block is grown on the surface of APTS-coated Fe3O4 nanoparticles by conventional growth approach of Michael addition/amidation reactions. The thus-obtained dendritic magnetite nanocarriers (DMNCs) were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM), atomic force microscopy (AFM), vibrating sample magnetometry(VSM), dynamic light scattering (DLS) and thermogravimetric (TGA) analysis. The functionalization of MNPs with the dendritic block was evident from FTIR and TGA analyses. The nanocarriers had an average size of 10 nm and exhibited superparamagnetism with high magnetization values at room temperature. The aqueous colloidal suspension of DMNCs (10 mg ml−1 of Fe) showed a temperature rise up to 43 °C in 5 min and yielded a moderate specific absorption rate (SAR) value of 30 W g−1 of magnetite under the influence of AC magnetic field of 10 kA m−1 and 425 kHz frequency. Biocompatibility of the developed nanocarriers was evaluated in vitro by assessing their cytotoxicity on human cervical cancer cells (HeLA cells) using a sulforhodamine B (SRB) assay. Encapsulation and release of the anticancer drug doxorubicin (DOX) was investigated. The change in surface charge, as evident from zeta potential analyzer and quenching of fluorescence intensity, strongly suggests the interaction of DOX with the DMNCs. The nanocarriers showed good capacity to encapsulate DOX, with loading as high as 65% (w/w) and a pH-responsive sustained release of 54% at pH 5.0. Also, the release of DOX from the nanocarriers increased up to 80% on application of an AC magnetic field.

Chemically or enzymatically modified low-density lipoproteins (LDL), with and without changes in surface charge, were studied in vivo in the healing, balloon catheter-deendothelialized rabbit aorta to determine the effect of LDL modification on its accumulation in arterial lesions. In this model, in which healing (reendothelialization) proceeds radially outward from individual aortic branch arteries, it was previously shown by autoradiography that two kinetically distinct compartments accumulated 125I-labeled LDL. In aortic regions which were still deendothelialized, accumulation was diffuse and labile. In contrast, at the edges of the islands of regenerating endothelium, LDL accumulation was intensely focal, as it is in human atherosclerotic lesions, and persisted for at least 40 h after injection in spite of falling levels of radiolabeled LDL in plasma [Chang, M. Y., et al. (1992) Arterioscler. Thromb. 12, 1088-1098]. In the present study, modified LDLs with gradations in charge change were prepared to clarify the role of changes in surface charge on focal aortic LDL accumulation. Oxidized LDL (weakly anionized), desialated LDL (weakly cationized), and reductively methylated LDL (no change in net charge) all accumulated focally. Focal accumulation of native LDL also occurred in ballooned rabbits fed probucol to inhibit LDL oxidation. Strongly anionized succinylated and diazobenzenearsonylated LDL and strongly cationized dimethylpropanediamine LDL did not accumulate focally. The results support the concept that focal sequestration of LDL in arterial lesions is mediated by specific, oxidation-independent patterns of charge and polarity on LDL which are disrupted by major changes in LDL surface charge.

In this study, the effects of different precursor concentrations on the growth and characteristics properties of the zinc oxide (ZnO) nanorods (NRs) synthesized by using modified and conventional chemical bath deposition (CBD) methods were investigated. The morphologic, structural and optical properties of synthesized ZnO NRs with different precursor concentrations were studied using various characterization techniques. The experimental results show that the varying precursor concentration of the reactants has a remarkable and significant effect on the growth and characteristics properties of ZnO NRs. In addition, the characteristic properties of ZnO NRs grown using the modified method showed significantly improved and enhanced properties. The average length of grown ZnO NRs increased with increased precursor concentration; it can be seen that longer ZnO NRs have been investigated using the modified CBD methods. The ZnO NRs synthesized at 0.05 M using the modified method were grown with high aspect ratios than the ZnO NRs grown using conventional means which were 25 and 11, respectively. The growth rate increased with increased precursor concentration; it can be observed that a higher growth rate was seen using the modification CBD method. Furthermore, XRD results for the two cases reveal that the grown ZnO samples were a nanorod-like in shape and possessed a hexagonal wurtzite structure with high crystal quality. No other phases from the impurity were observed. The diffraction peaks along (002) plane became higher, sharper and narrower as precursor concentration increased, suggesting that the crystalline quality of ZnO NRs grown using the modified method was more enhanced and better than conventional methods. However, optical studies show that the transmittance at each concentration was more than two times higher than the transmittance using the modified CBD method. In addition, optical studies demonstrated that the ZnO NRs grown by using modified and conventional methods had a direct Eg in the range of (3.2–3.26) eV and (3.15–3.19) eV, respectively. It was demonstrated in two methods that ZnO NRs grown at a precursor concentration 0.05 M gave the most favorable result, since the NRs had best characteristic properties.

The collection and transport of charges at the electrodes are the main factors limiting the efficiency of organic solar cells. Zinc oxide (ZnO) in nanostructured form helps to overcome this problem by introducing a ZnO buffer layer between the photoanode and the donor material. To achieve this, the ZnO thin film must exhibit good crystallinity, along with good electrical conductivity and high optical transparency in the visible range. The aim of this work is to investigate the effect of precursor sources and precursor concentrations on the structural, morphological, and optical properties of ZnO thin films. Three different precursor sources have been used: zinc acetate, zinc chloride and zinc nitrate. In each deposition solution, the precursor concentration varied from 0.1 M to 0.3 M. The ZnO films were deposited on glass substrates and all the films were annealed at 400°C for 3 hours. The structural, morphological and optical properties of deposited films were investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), and UV-visible spectroscopy respectively. XRD results showed that, regardless of the precursor source, all the ZnO films are polycrystalline with a hexagonal wurtzite structure. ZnO films obtained from acetate and nitrate sources crystallize preferentially along (002) and the peak intensity increases as the precursor concentration increases. SEM images showed that all the ZnO films are homogeneous, but films deposited from zinc acetate and zinc nitrate looked more compact and smoother than those obtained with zinc chloride which looked porous. UV-visible spectroscopy results revealed that the films transmittance depends both on precursor source and concentration. ZnO thin films deposited from zinc acetate at 0.3M concentration exhibit the best transmittance of 95% due to their smooth and uniform surfaces. The band gap of ZnO obtained from the zinc acetate precursor decreases with increasing solution concentration. It is found to be 3.29 eV, 3.26 eV, and 3.22 eV for concentrations of 0.1 M, 0.2 M, and 0.3 M, respectively. It therefore appears that ZnO films obtained from zinc acetate can be used as an electron transport layer for solar cells as they exhibit the best crystallinity and the highest transmittance.

Control of the shape and size of iron oxide (α-Fe2O3) nanoparticles synthesized through the chemical precipitation method

The presence of dyes in effluent poses various environmental as well as health hazards for many organisms. Although various remediation strategies have been implemented to reduce their effect, dyes still manage to infiltrate into the environment and hence new strategies are required to address some of the problems. This study investigated the innovation of two cationic water-soluble polymers viz., Proline-Epichlorohydrin-Ethylenediamine Polymer (PEP) and Thiazolidine-Epichlorohydrin-Ethylenediamine Polymer (TEP) that were used to remediate selected synthetic dyes from synthetic effluent by adsorption and dye reduction. Both polymers were synthesized using monomers of a secondary amine, epichlorohydrin and ethylenediamine and were subsequently characterized and modified and their remediation potential studied. In the first study, PEP was synthesized and characterized by 1H-NMR Spectroscopy, FT-IR Spectroscopy, dynamic light scattering, and thermogravimetric analysis (TGA). Thereafter PEP was modified with bentonite clay, by simple mixing of the reactants, to form a Proline-Epichlorohydrin-Ethylenediamine Polymer-bentonite composite (PRO-BEN); it was characterized by FT-IR Spectroscopy, scanning electron microscopy (SEM)/ energy dispersive X-ray spectroscopy (EDX), dynamic light scattering (DLS), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). Adsorption studies were then undertaken with a synthetic effluent containing three textile dyes, viz., Reactive Blue 222 (RB 222), Reactive Red 195 (RR 195) and Reactive Yellow (RY 145). Various conditions were investigated including pH of the solution, temperature, sodium chloride concentration, initial dye concentration and the dosage of adsorbent used. The experimental data for all dyes followed a Langmuir isotherm. The adsorption process was found to be pseudo-second order. According to the thermodynamic parameters, the adsorption of the dyes was classified as physisorption and the reaction was spontaneous and exothermic. The data were also compared using studies with alumina as an adsorbent. Results showed that PRO-BEN exhibited better absorptivity and desorption than alumina making its use a better recyclable remediation strategy for the removal of organic dyes in wastewater treatment plants. In the second study, TEP was synthesized and then characterized by FT-IR Spectroscopy, 1H-NMR Spectroscopy, TGA and DLS. Thereafter, TEP was used to prepare TEP capped gold nanoparticles (TEP-AuNPs). Herein, two methods were investigated: the Turkevich method and an adaptation of the Turkevich method using bagasse extract. The TEP-AuNPs was characterized by FT-IR Spectroscopy, SEM, EDX, DLS and TEM. Thereafter the reduction of each of Allura Red, Congo Red and Methylene Blue was investigated with the TEP-AuNPs for its catalytic activity toward dye reduction. This study showed that the batch of AuNPs prepared by the Turkevich method had higher rates of dye reduction compared with AuNPs prepared using bagasse extract. Also the quantity of TEP used as capping agent greatly influenced the size, shape and surface charge of the nanoparticles as well as their catalytic performance: the Vroman effect explained this behavior of the TEP-AuNPs. It was finally concluded that whilst PRO-BEN, in the first study, showed excellent dye remediation properties, the second study on TEP-AuNPs showed good catalytic activity for the reduction of selected dyes, however, it was more effective at lower polymer concentration. Finally, both materials displayed good potential for the clean-up of selected synthetic dyes from synthetic effluents.

In 2017 the field experiments were established at two localities of the South-west Slovakia (1 Doln Streda: sandy Arenosol and 2 Vek any: loamy Chernozem). The experiments involved biochar substrates (1 BS1 mix biochar, sheep manure and 2 BS2 mix biochar, sheep manure and digestate) in two application doses (10 and 20 t ha -1 ), which were applied independently compared with the unfertilized control (Co-NF) and combined with additional fertilization versus the fertilized control (Co-F), in order to verify their impacts on the changes of soil properties. In the spring and autumn of 2018-2020, within these experiments the soil samples were taken to determine the range of effect of the tested biochar substrates (BS) and also their combination with fertilization (F) on the changes of soil pH and surface charge of soil particles in the soils different in texture. The results pointed out the fact that a more significant effect of tested BS on soil pH was detected in sandy soil than loamy soil. In sandy soil, only the application of BS2 in doses 10 and 20 t ha -1 statistically significantly increased the soil pH in H 2 O in comparison with Co-NF. The application BS1 + F in dose 10 t ha -1 and BS2+F in dose 20 t ha -1 statistically significantly increased pH in KCl compared with Co-F. The fertilization to BS eliminated the considerable decrease of the soil pH in H 2 O both soils. In sandy soil, pH was substantially regulated by the content of alkali cations themselves in BS; however, in loamy soil, it occurred as a result of the increase of the content of soil organic carbon after the application of BS (R 2 = 0.339), but also BS + F (R 2 = 0.468). In sandy soil, the application of BS itself, owing to the change of the surface charge, influenced predominantly the sorption of anions. Conversely, the additional fertilization to BS treatments had an impact on the sorption of cations. In loamy soil, the application of BS and BS + F as a result of the change of surface charge did not have any significant effect on the total soil sorption.

PS-b-PAA nanovesicles coated by modified PEIs bearing hydrophobic and hydrophilic groups

In this work, polystyrene-b-poly (acrylic acid) (PS-b-PAA) nanovesicles were coated by modified chitosans aiming at studying its physicochemical parameters. The chitosan (CS) was chemically modified to add hydrophilic and/or hydrophobic groups, obtaining three modified chitosans. The PS-b-PAA nanovesicles were obtained by organic (1,4-dioxane) cosolvent method in water, resulting in nanovesicles with less than 150 nm of diameter (polydispersibility index - PDI at 90° = 0.106), measured by dynamic light scattering (DLS) and transmission electron microscopy (TEM), and negative zeta potential (-37.5 ± 3.2 mV), allowing the coating of its surface with oppositely charged polysaccharides, such as the CS and the modified chitosans. The coating process was made by mixing the colloidal suspensions with the CS and the modified chitosans at specific ENT#091;CS-xENT#093;/ENT#091;PS-b-PAAENT#093; ratios (0.001 to 1.0 wt %) and measuring the change in size and surface charge by DLS and zeta potential. Upon reaching maximum adsorption, the zeta potential parameter was positively stabilized (+26.7 ± 4.1 mV) with a hydrodynamic diameter slightly longer (< 200 nm of diameter). The encapsulation efficiency (EE) of minoxidil, quantified by capillary electrophoresis, was 50.7%, confirming their potential as drug delivery carriers and the coating process showed the possibility of controlling the surface charge nature of these nanovesicles.

Editorial FocusCharge of the mito brigade. Focus on "Changes in mitochondrial surface charge mediate recruitment of signaling molecules during apoptosis"George R. DubyakGeorge R. DubyakDepartment of Physiology and Biophysics, Case Western Reserve University, Cleveland, OhioPublished Online:01 Jan 2011https://doi.org/10.1152/ajpcell.00454.2010This is the final version - click for previous versionMoreSectionsPDF (44 KB)Download PDF ToolsExport citationAdd to favoritesGet permissionsTrack citations the role of mitochondria as the foci of apoptotic signaling events in physiological and pathological conditions is now well-established (12). Multiple studies have demonstrated the recruitment of various cytosolic effector proteins, such as caspase-8, Bax, and Bak, to the outer membrane surface of mitochondria in apoptotic cells. Other reports have documented the redistribution of pro-apoptotic proteins, such as cytochrome c and Smac/Diablo, from the intermembrane space to the mitochondrial outer membrane (MOM) or the cytosol. The assembly of these newly recruited or transferred proteins into apoptotic signaling complexes, such as the Bax/Bak-based pores that mediate MOM permeabilization, has also been extensively characterized. Although the mechanisms by which apoptotic effector proteins recognize the MOM as a specific subcellular platform remain incompletely understood, recent studies have identified cardiolipin (CL), a predominantly mitochondrial phospholipid, as a key "targeting" factor (4, 6, 13). Both tBid (the pro-apoptotic truncated form of Bid) and caspase-8 bind to CL and disruption of these CL-effector protein interactions markedly attenuates the progression of apoptosis. Notably, association of these pro-apoptotic proteins with CL can involve stereospecific sites such as the hairpin motif within tBid formed by its α-6 helix (αH6) domain but independent of its BH3 domain (5, 11). However, CL is also dianionic at physiological pH and thus contributes to the overall surface charge of membranes in which it is abundant. In this issue of AJP-Cell Physiol, Heit et al. (8) report that mitochondria rapidly gain negative surface charge, likely due to increased CL in the outer membrane, during the early phases of apoptosis. Based on CL neutralization approaches, this study from Grinstein's group supports a novel and mechanistically significant model wherein mitochondrial exposure of negatively charged CL facilitates the electrostatic recruitment of multiple cationic proteins required for the progression of critical apoptotic signaling events.Background Illumination: Fluorescent Chimeric Proteins as Reporters of Specific Lipids and Surface Change in Subcellular Membrane Compartments During PhagocytosisThat mitochondrial CL can act as both a selective partner for particular proteins and a determinant of net charge on membrane surfaces is analogous to the capacity of inositol phospholipids both to bind proteins with specific structural motifs (e.g., PH or FYVE domains) and to contribute to the overall electronegativity of the plasma membrane inner leaflet (3). Identification of an increasing number of proteins that recognize specific phosphatidylinositol (PtdIns) subtypes {e.g., phosphatidylinositol (4,5) bisphosphate [PtdIns(4,5)P2] vs. phosphatidylinositol (3,4,5) trisphosphate [PtdIns(3,4,5)P3]} has facilitated the generation of fluorescent chimeric protein probes for interrogating the subcellular localization and abundance of these lipids in intact cells under basal conditions or in response to various stimuli (Table 1). Indeed, the Grinstein group has previously provided major technical and conceptual contributions to defining the dynamics of lipid localization, metabolism, and redistribution during phagocytosis by macrophages (7, 16, 18). Those studies revealed a transient increase, followed a sustained decrease, in plasma membrane PtsIns(4,5)P2 that was correlated with a transient increase in PtdIns(3,4,5)P3 within the forming phagocytic cup. Notably, although neither PtsIns(4,5)P2 nor PtdIns(3,4,5)P3 was present within the fully internalized phagosome, a third inositide [PtsIns(3)P] was abundant. These localized changes in PtdIns subtypes reflected complex temporal changes in the activities of inositol kinases, inositol phosphatases, and phospholipases that target PtdIns species. The changes in inositide metabolism and localization were not merely epiphenomena because their perturbation by pharmacological or genetic approaches markedly affected the progression of phagosome formation and trafficking.Table 1. Subcellular lipids: localization and recruitment of signaling proteins via specific or electrostatic interactionsLipidSubcellular Content (Basal)Subcellular Content (Growth Stimulation; Endocytosis; Phagocytosis)Subcellular Content (Apoptosis)Specific Protein-Binding Domain(s)Major Contribution to Surface Charge (State-Dependent)Specific vs. Electrostatic Binding of Signaling ProteinsPtdIns(3)PPM-inner: lowPM-inner: highPM-inner: lowFYVE-EEA1No in PMSpecific: PIK-FYVEPM-outer: lowPM-outer: lowPM-outer: lowNo in endosomeEndosomes: lowEndosomes: low>highEndosomes: lowNo in MitoElectrostatic:?Mito: noMito: noMito: noPtdIns(4,5)P2PM-inner: highPM-inner: lowPM-inner: highPH-PLCδYes in PMSpecific: PLCδPM-outer: lowPM-outer: lowPM-outer: lowNo in endosomeEndosomes: lowEndosomes: lowEndosomes: lowNo in MitoElectrostatic: K-Ras; Rac1; c-Src; PI(4)P-5K in PMMito: noMito: noMito: noPtdIns(3,4,5)P3PM-inner: lowPM-inner: highPM-inner: lowPH-AktNo in PMSpecific: Akt; Gab2PM-outer: lowPM-outer: lowPM-outer: lowPH-Gab2Yes in endosomeEndosomes: lowEndosomes: high>lowEndosomes: lowNo in MitoElectrostatic:?Mito: noMito: noMito: noPtdSerPM-inner: highPM-inner: lowPM-inner: lowC2-lactadherinYes in PMSpecific: annexin V in apoptotic cellsPM-outer: lowPM-outer: highPM-outer: highYes in endosomeEndosomes: highEndosomes: highEndosomes: highNo in MitoElectrostatic: K-Ras; Rac1; c-Src; PI(4)P-5K in PMMito: noMito: noMito: noDiacyl glycerolPM-inner: lowPM-inner: highPM-inner:?C1-PKCNo in PMSpecific: PKCPM-outer: lowPM-Outer: lowPM-outer:?C1-PKDNo in endosomeEndosomes: medEndosomes: high>lowEndosomes:?No in MitoElectrostatic: noneMito: lowMito:lowMito:lowCardiolipinPM: noPM: noPM: noCLBD-mitoCKNo in PMSpecific: mitoCK; cytoC; caspase-8?; Bid?;Endosomes: noEndosomes: noEndosomes: noNo in endosomeMito-IM: highMito-IM: highMito-IM: lowYes in MitoMio-OM: lowMio-OM: lowMio-OM: highElectrostatic: Bax/Bak?; K-Ras?Subcellular localization of lipids and proteins with lipid-specific binding domains. PM, plasma membrane; Mito, mitochondria; IM, inner membrane; OM, outer membrane; PH, pleckstrin homology; FYVE, Fab1-YOTB-Vac1-EEA1; EEA1, early endosome antigen 1; PLC, phospholipase C; PKC, protein kinase C; PKD, protein kinase D; CLBD; cardiolipin binding domain; CK, creatine kinase.Another offshoot of these analyses of phospholipid dynamics during phagocytosis was consideration of how the quantitative and qualitative changes in the different inositide species within forming versus internalized phagosomes alters the surface charge of these membrane compartments (15–17). The pioneering insights and studies of Stuart McLaughlin and colleagues during the 1980s (and continuing to the present) demonstrated that the headgroups of anionic phospholipids within a membrane leaflet can provide sufficient local negative charge to markedly concentrate inorganic and organic cations, including proteins, at membrane surfaces (1, 2, 9, 10, 14). In this regard, the various inositide species are not equivalent. Thus, while PtsIns(3)P may be the major inositide in fully internalized phagosomes/endosomes, it is less anionic than the PtsIns(4,5)P2 and PtdIns(3,4,5)P3 species, which predominate (albeit with multiphasic dynamics) in the developing phagocytic cup. This motivated subsequent studies by Grinstein and colleagues to generate chimeric fluorescent protein probes (which include varying lengths of polybasic amino acid stretches plus isoprenoid membrane targeting motifs) that could report local electronegative surface charges during formation and maturation of phagosomes/endosomes (7, 17).These analyses revealed that, despite the large qualitative and quantitative changes in inositide species, the surface charge of fully internalized phagosomes was only modestly less electronegative than that of the resting plasma membrane or the developing phagocytic cup. This was correlated with the presence of high concentrations of phosphatidylserine (PtdSer), a noninositide but anionic lipid, in the early and mature phagosome (15, 17). The Grinstein lab also generated a PtdSer-specific fluorescent reporter based on a discoidin C2 domain from lactadherin that stereoselectively binds to PtdSer. Armed with this impressive array of lipid-specific probes and surface charge reporters, these investigators have been able to demonstrate that changes in subcellular lipid dynamics generate a matrix of coincidence detection-type signals for the recruitment of multiple signaling proteins that contain stereoselective lipid recognition domains or polybasic motifs that can be electrostatically "titrated" onto membrane surfaces with graded differences in negative surface charge. Notably, these polybasic proteins include a variety of molecular switch signaling proteins, such as small GTPases (e.g., K-Ras and Rac1) and protein tyrosine kinases (c-Src) that exert pleiotropic effects on integrated cell function (7).Flash Forward: Fluorescent Chimeric Proteins as Reporters of Specific Lipids and Surface Change in the MOM During ApoptosisHeit et al. (8) have now used this toolbox of fluorescent lipid and surface charge reporters to monitor the biochemistry and biophysics of the MOM surface in intact cells during the progression of apoptosis. Their key findings include: 1) characterization of apoptotic cells by redistribution of R-Pre, a polyarginine-based sensor of relative surface charge, from the plasma membrane (where this probe predominantly localizes in control cells) to the mitochondrial surface. 2) The apoptosis-related association of R-Pre with mitochondria was not mimicked in cells treated with the Ca2+ ionophore ionomycin which, via the phospholipase C-mediated hydrolysis of PtdIns(4,5)P2 and scramblase-regulated flip of PtdSer to the extracellular leaflet, decreases surface charge of the plasma membrane cytosolic leaflet and, as a consequence, the association of R-Pre with that membrane surface. 3) The increased negative surface charge was also observed in isolated mitochondria treated with purified tBid, which elicits an "apoptotic" phenotype in mitochondria under in vitro cell-free conditions. 4) The increased electronegativity of in situ mitochondria was not correlated with increased levels of PtdIns(4,5)P2, PtdIns(3,4,5)P3, or PtdSer in the cytosolic face of the MOM but was correlated with an increased content of CL. [This latter finding was facilitated by generation of another lipid-selective sensor probe based on the CL-binding domain (CLBD) of mitochondrial creatine kinase.] 5) The increases in mitochondrial surface CL and electronegativity preceded other early indices of apoptotic progression, such as PtdSer redistribution to the extracellular surface or MOM permeabilization. 6) The increased mitochondrial electronegativity elicited association of fluorescence-tagged polybasic signaling proteins, such as K-Ras, with the mitochondrial surface.The most notable finding was that neutralization of the increased MOM CL by overexpressed CLBD protein markedly impaired the initiation and progression of apoptosis, presumably by shielding or masking the negative charge of CL. This strongly suggests that recruitment of key apoptotic effector proteins to the mitochondria may be largely driven by electrostatic associations linked to the increased redistribution of dianionic CL to the cytosolic face of the MOM.These findings raise several questions that will motivate additional experiments to further extend and support this scenario. What is the source and initiating mechanism for the increased CL distribution to the mitochondrial surface? Might other anionic phospholipids, such as phosphatidic acid, also contribute to the altered surface charge of apoptotic mitochondria? What are the key apoptotic effector proteins that use electrostatic association for targeting to the mitochondrial compartment? Might yet-to-be identified polybasic proteins or cationic small molecule regulators modulate mitochondrial apoptotic signaling as a consequence of electrostatic recruitment? Stay tuned for the conclusion of this electrifying story.GRANTSThis paper was supported in part by National Institutes of Health R01-GM-36387.DISCLOSURESNo conflicts of interest, financial or otherwise, are declared by the author(s).REFERENCES1. Andersen OS , Feldberg S , Nakadomari H , Levy S , McLaughlin S. Electrostatic interactions among hydrophobic ions in lipid bilayer membranes. Biophys J 21: 35–70, 1978.Crossref | PubMed | ISI | Google Scholar2. Balasubramanian A , McLaughlin S. Electro-osmosis at the surface of phospholipid bilayer membranes. Biochim Biophys Acta 685: 1–5, 1982.Crossref | PubMed | ISI | Google Scholar3. Goldenberg NM , Steinberg BE. Surface charge: a key determinant of protein localization and function. Cancer Res 70: 1277–1280, 2010.Crossref | PubMed | ISI | Google Scholar4. Gonzalvez F , Gottlieb E. Cardiolipin: setting the beat of apoptosis. Apoptosis 12: 877–885, 2007.Crossref | PubMed | ISI | Google Scholar5. 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Am J Physiol Cell Physiol (October 6, 2010). doi:10.1152/ajpcell.00139.2010.PubMed | ISI | Google Scholar9. Langner M , Cafiso D , Marcelja S , McLaughlin S. Electrostatics of phosphoinositide bilayer membranes. Theoretical and experimental results. Biophys J 57: 335–349, 1990.Crossref | PubMed | ISI | Google Scholar10. McLaughlin S , Harary H. The hydrophobic adsorption of charged molecules to bilayer membranes: a test of the applicability of the stern equation. Biochemistry 15: 1941–1948, 1976.Crossref | PubMed | ISI | Google Scholar11. Petit PX , Dupaigne P , Pariselli F , Gonzalvez F , Etienne F , Rameau C , Bernard S. Interaction of the alpha-helical H6 peptide from the pro-apoptotic protein tBid with cardiolipin. FEBS J 276: 6338–6354, 2009.Crossref | PubMed | ISI | Google Scholar12. Smith DJ , Ng H , Kluck RM , Nagley P. The mitochondrial gateway to cell death. IUBMB Life 60: 383–389, 2008.Crossref | PubMed | ISI | Google Scholar13. 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Yeung T , Heit B , Dubuisson JF , Fairn GD , Chiu B , Inman R , Kapus A , Swanson M , Grinstein S. Contribution of phosphatidylserine to membrane surface charge and protein targeting during phagosome maturation. J Cell Biol 185: 917–928, 2009.Crossref | PubMed | ISI | Google Scholar18. Yeung T , Terebiznik M , Yu L , Silvius J , Abidi WM , Philips M , Levine T , Kapus A , Grinstein S. Receptor activation alters inner surface potential during phagocytosis. Science 313: 347–351, 2006.Crossref | PubMed | ISI | Google ScholarAUTHOR NOTESAddress for reprint requests and other correspondence: G. R. Dubyak, Dept. of Physiology and Biophysics, Case Western Reserve Univ., School of Medicine, 1900 Euclid Ave., Cleveland, OH 44106 (e-mail: george.[email protected]edu). 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This study reports the successful extracellular biosynthesis of lead sulfide (PbS) nanoparticles using non-motile, Gram-variable Micrococcus luteus bacteria. Optimization studies revealed optimal growth conditions for bacterial biomass and PbS production at room temperature, pH 7, and 96h of incubation. The influence of precursor concentration on the growth and properties of PbS nanostructures was investigated. Characterization techniques, including X-ray diffraction, scanning electron microscopy, and FTIR spectroscopy, confirmed the formation of spherical, pure-phase PbS nanoparticles with sizes ranging from 150 to 250nm. UV-visible absorption spectroscopy demonstrated strong absorption in the near-infrared region, indicative of the bandgap of PbS. Furthermore, an increase in precursor concentration resulted in a blue shift of the band gap. Utilizing these biogenic PbS nanoparticles, a high-performance photodetector device was fabricated with the architecture FTO/TiO2/PbS/PANI/NiS/V2O5/Pt. The device exhibited excellent stability and repeatability in ON-OFF switching cycles, with a high detectivity of 30.9 × 107 Jones and fast response times of 0.94s (rise time) and 0.478s (decay time). These findings demonstrate the potential of biogenic PbS nanoparticles for developing high-performance optoelectronic devices.

The need to characterize nanoparticles in solution before assessing the in vitro toxicity is a high priority. Particle size, size distribution, particle morphology, particle composition, surface area, surface chemistry, and particle reactivity in solution are important factors which need to be defined to accurately assess nanoparticle toxicity. Currently, there are no well-defined techniques for characterization of wet nanomaterials in aqueous or biological solutions. Previously reported nanoparticle characterization techniques in aqueous or biological solutions have consisted of the use of ultra-high illumination light microscopy and disc centrifuge sedimentation; however, these techniques are limited by the measurement size range. The current study focuses on characterizing a wide range of nanomaterials using dynamic light scattering (DLS) and transmission electron microscopy, including metals, metal oxides, and carbon-based materials, in water and cell culture media, with and without serum. Cell viability and cell morphology studies were conducted in conjunction with DLS experiments to evaluate toxicological effects from observed agglomeration changes in the presence or absence of serum in cell culture media. Observations of material-specific surface properties were also recorded. It was also necessary to characterize the impact of sonication, which is implemented to aid in particle dispersion and solution mixture. Additionally, a stock solution of nanomaterials used for toxicology studies was analyzed for changes in agglomeration and zeta potential of the material over time. In summary, our results demonstrate that many metal and metal oxide nanomaterials agglomerate in solution and that depending upon the solution particle agglomeration is either agitated or mitigated. Corresponding toxicity data revealed that the addition of serum to cell culture media can, in some cases, have a significant effect on particle toxicity possibly due to changes in agglomeration or surface chemistry. It was also observed that sonication slightly reduces agglomeration and has minimal effect on particle surface charge. Finally, the stock solution experienced significant changes in particle agglomeration and surface charge over time.

In this paper the fate (as size and surface charge changes) of Stober silica based nanoparticles in contact with a growth medium is studied through dynamic light scattering (DLS), ζ-potential analyser and electronic microscopy, both scanning (SEM) and transmission (TEM). The experimental results confirm that biomacromolecules corona rapidly forms on NP incubated after dispersion in biological environments. They also suggest that: interactions with the components of the growth media may reverse the Stober particles aggregation process, giving smaller disaggregated particles bringing a biomacromolecules corona. At longer incubation time the particles slightly grow because of biomacromolecules interlocking. Incubation temperature and growth medium concentrations strongly affect the nanoparticles fate. In fact overnight incubation at 4 °C of particles dispersed into reconstituted EPILIFE growth medium diluted with water in a ratio 50/50 produces a corona compositionally and/or structurally different than the one formed during incubation at 37 °C of particles dispersed into reconstituted EPILIFE. However when the first ones are redispersed into reconstituted EPILIFE and incubated at 37 °C a change in the corona composition/structure does occur; at long times particles are obtained of similar hydrodynamic radius and ζ-potential than the ones produced after direct dispersion into reconstituted EPILIFE and incubation at 37 °C. DLS and ζ-potential measurements appear to be valuable tools to study the fate of nanoparticles in biological environments with the further advantage, with respect to SEM and TEM, that the nanoparticles are not exposed to the risk of clustering during samples preparation because of solvent evaporation.

To obtain a better understanding of the short term reactions between sulfate and hydrous alumina the relationships between the amount of sulfate retained by the alumina and reaction time, concentration, ligands displaced by sulfate, and changes in surface charge were studied. Experimental conditions were 3 hours reaction time, 0.01 M NaCl medium, pH 5.0, 30°C, and nitrogen atmosphere. Sulfate adsorption was very rapid and about 90% of the reaction was over in 10 min. There was little change in adsorption after 3 hours. The adsorption increased with increasing final solution concentration up to about 6 µeq/ml after which it decreased. Sulfate adsorption resulted in the release of OH ‐ from, and the neutralization of positive charge on the surface. From the quantitative relationships between sulfate adsorbed, the ligands displaced, and the changes in surface charge it is proposed that sulfate is adsorbed on hydrous alumina as SO 4 2‐ bridging across two aluminum atoms, forming a six‐membered ring. At low concentrations sulfate preferentially displaces aquo groups (Al‐OH 2 ) from the positive sites. With increasing concentration, increasing proportions of hydroxo groups (Al‐OH) from the neutral sites are displaced. The decrease in adsorption above 6 µeq/ml of sulfate concentration is inexplicable at this stage.