Surface Plasmon Resonance Response Research Articles

On the Use of Surface Plasmon Resonance-Based Biosensors for Advanced Bioprocess Monitoring

Biomanufacturers are being incited by regulatory agencies to transition from a quality by testing framework, where they extensively test their product after their production, to more of a quality by design or even quality by control framework. This requires powerful analytical tools and sensors enabling measurements of key process variables and/or product quality attributes during production, preferably in an online manner. As such, the demand for monitoring technologies is rapidly growing. In this context, we believe surface plasmon resonance (SPR)-based biosensors can play a role in enabling the development of improved bioprocess monitoring and control strategies. The SPR technique has been profusely used to probe the binding behavior of a solution species with a sensor surface-immobilized partner in an investigative context, but its ability to detect binding in real-time and without a label has been exploited for monitoring purposes and is promising for the near future. In this review, we examine applications of SPR that are or could be related to bioprocess monitoring in three spheres: biotherapeutics production monitoring, vaccine monitoring, and bacteria and contaminant detection. These applications mainly exploit SPR’s ability to measure solution species concentrations, but performing kinetic analyses is also possible and could prove useful for product quality assessments. We follow with a discussion on the limitations of SPR in a monitoring role and how recent advances in hardware and SPR response modeling could counter them. Mainly, throughput limitations can be addressed by multi-detection spot instruments, and nonspecific binding effects can be alleviated by new antifouling materials. A plethora of methods are available for cell growth and metabolism monitoring, but product monitoring is performed mainly a posteriori. SPR-based biosensors exhibit potential as product monitoring tools from early production to the end of downstream processing, paving the way for more efficient production control. However, more work needs to be done to facilitate or eliminate the need for sample preprocessing and to optimize the experimental protocols.

The base and root of domain II loops of Cry toxins contribute to binding to Bombyx mori ABC transporter C2.

Little information is available regarding the region of Cry toxins involved in binding to their major receptors, the ATP-binding cassette (ABC) transporters. We analyzed which Cry1Aa amino acid residues contribute to binding to Bombyx mori ABC transporter C2 (BmABCC2). Several two oxidized double-cysteine substitution mutant toxins were made. In these, two amino acids at distant positions on toxin loop α8 and loop 2 or loop 2 and loop 3 were substituted with cysteine residues and crosslinked. These mutants exhibited a marked reduction in binding affinity to BmABCC2, suggesting that the binding site comprises complex cavities formed by loops α8, 2, and 3. Loop swapping between Cry1Aa and other BmABCC2-incompatible toxins indicated that loop 2 acts as a binding affinity-generating part of Cry1Aa toxin. Using single amino acid substitution mutants, the results of surface plasmon resonance (SPR) analysis and response assays with BmABCC2-expressing Sf9 cells indicated that Y366, R367, R368, and L447 in the Cry1Aa root and base region of loops 2 and 3 play important roles in binding. Furthermore, SPR analyses of these mutants suggested that a two-state binding model fits best the data obtained. Moreover, complex cavities and the above-mentioned amino acid residues contribute to the generation of multiple binding points and high-affinity binding. Finally, we found that the binding site of B. mori cadherin-like protein consists of complex cavities comprising loops 1, 2, and 3, partially overlapping that of BmABCC2, suggesting that the loop region of Cry1Aa toxin acts as a promiscuous binding site.

Flexible and Ultrathin Metal-Oxide Films for Multiresonance-Based Sensors in Plastic Optical Fibers

We have exploited a laser-based integration process of ultrathin metal-oxide (MO) films to improve the plasmonic effect in sensors based on D-shaped plastic optical fibers (POFs). More specifically, using ultrathin MO films, the performances of the surface plasmon resonance (SPR) phenomenon improve and a lossy mode resonance (LMR) can occur. Although the role of this kind of materials has been already presented, when they are deposited as overlayer (upside the thin metal film), we have used a different approach by depositing MOs, especially zirconium oxide (ZrO2) and titanium oxide (TiO2), as flexible intermediate layers between the exposed core of POFs and the gold film. The MO layer is prepared from sol–gel solution, and deep-UV laser curing allows us to densify the thin film and tune the refractive index, with a room-temperature process fully compatible with the flexible polymer substrates. In a preliminary step, we have carried out numerical results, based on transfer matrix formalism, to predict the SPR response. Subsequently, we have experimentally characterized the developed sensor configurations. Numerical and experimental results have shown above all an enhancement of the sensor performances, in terms of SPR sensitivity, with respect to a reference sensor based on a polymer instead of MOs. Moreover, in some proposed sensor configurations, together with the SPR phenomenon, an LMR phenomenon was observed. It occurred in a different wavelength range, for a typical refractive index range present when considering receptors for biochemical sensing applications. Therefore, both resonances (SPR and LMR) could be used in several application fields.

Photoswitchable Machine-Engineered Plasmonic Nanosystem with High Optical Response for Ultrasensitive Detection of microRNAs and Proteins Adaptively

Modulating optoelectronic properties of inorganic nanostructures tethered with light-responsive molecular switches by their conformational change in the solid state is fundamentally important for advanced nanoscale-device fabrication, specifically in biosensing applications. Herein, we present an entirely new solid-state design approach employing the light-induced reversible conformational change of spiropyran (SP)-merocyanine (MC) covalently attached to gold triangular nanoprisms (Au TNPs) via alkylthiolate self-assembled monolayers to produce a large localized surface plasmon resonance response (∼24 nm). This shift is consistent with the increase in thickness of the local dielectric shell-surrounded TNPs and perhaps short-range dipole-dipole (permanent and induced) interactions between TNPs and the zwitterionic MC form. Water contact angle measurement and Raman spectroscopy characterization unequivocally prove the formation of a stable TNP-MC structural motif. Utilizing this form, we fabricated the first adaptable nanoplasmonic biosensor, which uses an identical structural motif for ultrasensitive, highly specific, and programmable detection of microRNAs and proteins at attomolar concentrations in standard human plasma and urine samples, and at femtomolar concentrations from bladder cancer patient plasma (n = 10) and urine (n = 10), respectively. Most importantly, the TNP-MC structural motif displays a strong binding affinity with receptor molecules (i.e., single-stranded DNA and antibody) producing a highly stable biosensor. Taken together, the TNP-MC structural motif represents a multifunctional super biosensor with the potential to expand clinical diagnostics through simplifying biosensor design and providing highly accurate disease diagnosis.

Surface plasmon resonance aptasensor based on niobium carbide MXene quantum dots for nucleocapsid of SARS-CoV-2 detection.

A novel label-free surface plasmon resonance (SPR) aptasensor has been constructed for the detection of N-gene of SARS-CoV-2 by using thiol-modified niobium carbide MXene quantum dots (Nb2C-SH QDs) as the bioplatform for anchoring N-gene-targeted aptamer. In the presence of SARS-CoV-2 N-gene, the immobilized aptamer strands changed their conformation to specifically bind with N-gene. It thus increased the contact area or enlarged the distance between aptamer and the SPR chip, resulting in a change of the SPR signal irradiated by the laser (He-Ne) with the wavelength (λ) of 633 nm. Nb2C QDs were derived from Nb2C MXene nanosheets via a solvothermal method, followed by functionalization with octadecanethiol through a self-assembling method. Subsequently, the gold chip for SPR measurements was modified with Nb2C-SH QDs via covalent binding of the Au-S bond also by self-assembling interaction. Nb2C-SH QDs not only resulted in high bioaffinity toward aptamer but also enhanced the SPR response. Thus, the Nb2C-SH QD-based SPR aptasensor had low limit of detection (LOD) of 4.9 pg mL−1 toward N-gene within the concentration range 0.05 to 100 ng mL−1. The sensor also showed excellent selectivity in the presence of various respiratory viruses and proteins in human serum and high stability. Moreover, the Nb2C-SH QD-based SPR aptasensor displayed a vast practical application for the qualitative analysis of N-gene from different samples, including seawater, seafood, and human serum. Thus, this work can provide a deep insight into the construction of the aptasensor for detecting SARS-CoV-2 in complex environments.Graphical abstract A novel label-free surface plasmon resonance aptasensor has been constructed to detect sensitively and selectively the N-gene of SARS-CoV-2 by using thiol-modified niobium carbide MXene quantum dots as the scaffold to anchor the N-gene-targeted aptamer.Supplementary InformationThe online version contains supplementary material available at 10.1007/s00604-021-04974-z.

Highly Sensitive Nitrogen Dioxide Sensor Based on Enhancement of Surface Plasmon Resonance Response in Glass Waveguides by C–Ag Nanodots

Highly Sensitive Nitrogen Dioxide Sensor Based on Enhancement of Surface Plasmon Resonance Response in Glass Waveguides by C–Ag Nanodots

(Invited) Photoelectrochemical Methanol Oxidation Under Visible and UV Excitation of TiO2-Supported TiN and Zrn Plasmonic Nanoparticles

TiN and ZrN nanoparticles (NPs) are an emerging class of plasmonic materials that can be used for harvesting energy of visible light in order to drive chemical reactions on the photocatalyst surface [1-3]. These refractory NPs effectively absorb light over l = 450-1200 nm, covering most of the solar spectrum. Both TiN and ZrN have the optical appearence of gold, but with the advantages of thermal stability, corrosion resistance and low cost. Previous theoretical and experimental research have shown that TiN does not exhibit as strong of a plasmonic resonance as gold (broader response, sample variability due to defect-dependent metallicity) [2, 4]. ZrN is expected to have a sharper blue-shifted local surface plasmon resonance (LSPR) response in comparison to TiN [4, 5]. Indeed, this theoretical prediction was verified by observation of a sharp plasmonic maximum for ZrN NPs decorated by a thin layer of SiN [4]. However, ZrN NPs appear to be less chemically inert owing to zirconium’s strong affinity for oxygen. A layer of dielectric ZrO2 forms on the surface of ZrN NPs even in the presence of trace oxygen. The oxide layer has a detrimental effect on the LSPR, leading to its broadening and red-shifting [5].Herein both experimental and computational approaches are used in order to optimize the performance of TiO2-supported TiN and ZrN NPs towards photoelectrochemical methanol (CH3OH) oxidation under visible excitation. UV excitation is utilized in order to provide complementary information on the interaction between photogenerated carriers at the plasmonic NP/semiconductor interface.The effects of plasmonic catalyst loading and applied potential were examined. Reaction products were determined by gas chromatography-mass spectrometry analysis of ZrN/TiO2 and TiN/TiO2 aqueous suspensions. Optical spectra for both TiN and ZrN NPs were computed using COMSOL including calculations of these NPs in solution and embedded in a TiO2 matrix. To examine the effect of oxide layer, the NPs were decorated with the corresponding oxide layers.ZrN NPs were synthesized by ammonolysis of Zr(NMe2)4. Clean Zr(NMe2)4 was prepared following a protocol from the literature [6]. In-house made ZrN powder and commercial TiN NPs (PlasmaChem) were dispersed into a P25 TiO2 matrix via the sonochemically mediated mixing of the transition metal nitride and TiO2 NPs in 50:50 (v/v) H2O:ethanol mixture overnight. The resulting photocatalysts contained 0.5 - 5 wt. % loadings of TiN and ZrN on TiO2. The ZrN/TiO2, TiN/TiO2 and bare TiO2 films for photoelectrochemical experiments were prepared by drop-casting 60 mL of ink comprising 20 mg of the photocatalyst, 30 ml of 5 wt% Nafion solution (Ion Power), 2.96 ml H2O and 0.74 ml iso-propanol, on FTO slide (coated surface area of 0.385 cm2). Experiments were conducted in a three-electrode photoelectrochemical cell. The photocatalyst films deposited on FTO-coated glass substrates served as working electrodes, while Pt foil and Ag/AgCl in 3 M NaCl (BioLogic, Inc) were used as counter and reference electrodes, respectively. Nine single-color LED lights were employed for illumination. The intensities varied between 10-100 mW/cm2, and 300-480 mW/cm2 in the wavelength range of 490-670 and 730-960 nm, respectively.Our results indicate that optical properties and photocatalytic activity of ZrN/TiO2 are strongly affected by ZrN surface oxidation and agglomeration. We found that under visible illumination, both in-house synthesized 17 nm ZrN and commercial 30 nm TiN NPs promote TiO2 activity for CH3OH oxidation, while under visible + UV excitation, an inhibition effect is observed. The differences between the TiN/TiO2 and ZrN/TiO2 interfaces are discussed and the mechanisms of promotion/inhibition of TiO2 photocatalytic activity by ZrN and TiN NPs are proposed.

Light-Activated Chemoresistive and Plasmonic-Resonant Optical Sensors for NO2 and H2 Sensing Based on ZnO Doped Nanoparticles

Light-Activated Chemoresistive and Plasmonic-Resonant Optical Sensors for NO2 and H2 Sensing Based on ZnO Doped Nanoparticles

Electrochemistry-Assisted Surface Plasmon Resonance Biosensor for Detection of CA 15-3.

In this work, we describe an innovative methodology based on combined surface plasmon resonance (SPR) and electrochemical responses (eSPR) in the same immunoassay for screening CA 15-3 cancer biomarker with high sensitivity (and selectivity), in a very simple, label-free, accurate, and fully automated manner. Detection was achieved by performing two simple steps. In the first step, direct SPR was used to monitor CA 15-3 interaction with surface immobilized antibody. Two linear response ranges were obtained and the detection limit achieved is poor (LOD of 21 U mL-1). However, in the second detection step, electrochemical measurements at the SPR gold surface were performed to measure the decrease of redox probe peak current upon antigen-antibody interaction, providing a suitable amplification strategy to lower detection levels of CA 15-3 (LOD of 0.0998 U mL-1), without the need of additional complex and/or expensive amplification steps to enhance the sensitivity. Moreover, selectivity studies were performed against other common cancer biomarkers and the results showed that the eSPR immunosensor is selective for the CA 15-3 protein. Finally, the clinical applicability of the developed eSPR biosensing methodology was successfully applied to detect CA 15-3 in human serum samples at clinically relevant levels due to the high sensitivity of electrochemical readout. The same concept may be further extended to other proteins of interest.

In Situ Imaging of Cellular Reactive Oxygen Species and Caspase-3 Activity Using a Multifunctional Theranostic Probe for Cancer Diagnosis and Therapy.

In this work, a multifunctional theranostic nanoprobe (Au-Ag-HM) was skillfully designed for simultaneous imaging of intracellular reactive oxygen species (ROS) and caspase-3 activity. The Au-Ag-HM was fabricated by coloading of silver nanoparticles (AgNPs) and hematoporphyrin monomethyl ether (HMME) to Au nanoflowers (AuNFs). When Au-Ag-HM was devoured by cancer cells, HepG2 cells were used as the model, and under laser irradiation, the photogenerated intracellular ROS by the photosensitizer HMME would induce the apoptosis of cancer cells. Meanwhile, the intracellular ROS triggered the oxidative etching of AgNPs on Au-Ag-HM, which led to a tremendous localized surface plasmon resonance response and scattering color changes in Au-Ag-HM, allowing in situ dark-field imaging of the ROS level in cancer cells. On the other hand, the ROS-induced activation of cellular caspase-3, which cleaved the C-peptide-containing caspase-3-specific recognition sequence (DEVD) and allowed HMME to release from the nanoprobe, resulted in a significant fluorescence recovery related to caspase-3 activity. Both photogenerated ROS and enhanced caspase-3 activity contributed to the synergistic effect of laser-mediated chemotherapy and photodynamic therapy. Therefore, the as-prepared theranostic probe could be used for simultaneous detection of cellular ROS and caspase-3 activity, distinguishing between tumor cells and normal cells, inducing the apoptosis of cancer cells, and providing a new method for diagnosis and therapy of cancer.

NIR enhanced peroxidase-like activity of Au@CeO2 hybrid nanozyme by plasmon-induced hot electrons and photothermal effect for bacteria killing

The antibacterial application of nanozyme relies on high catalytic efficiency and advanced functions. Plasmon stimulation represents an appealing way to modulate the enzyme-like function, but the utilization efficiency of plasmon excitation remained relatively low. Herein, by selective deposition of a ceria nanozyme on the ends of Au nanorods, we reported a dumbbell-shaped Au@CeO2 hybrid nanozyme with strong surface plasmon resonance (SPR) response in NIR range. This spatially separated structure can simultaneously harvest the plasmon-induced hot carriers and thermal effect, and results in significantly enhanced peroxidase-like activity of Au@CeO2 upon 808 nm irradiation. By using ultrafast transient absorption and in situ irradiation XPS technique, the hot electrons transfer behavior from Au to CeO2 and leading to the change of Ce3+/Ce4+ ratio are disclosed as the main contribution to the activity enhancement. Benefiting from enhanced peroxidase-like activity, Au@CeO2 exhibits efficient broad-spectrum antibacterial activity under NIR irradiation. These results indicate a spatio-temporal way to optimize enzyme-like activity through efficient use of plasmon excitation will be value for improving antibacterial efficacy.

Modulating surface plasmon resonance response by an external electromagnetic wave

We fabricated a highly sensitive layered structure of organic molecules and studied the influence of polarization of the external electromagnetic (EM) wave on the surface plasmon resonance response from the layered structure. The layered structure was formed by depositing a self-assembled monolayer (SAM) of mercaptoundecanoic acid (MUA) followed by a single layer of Langmuir-Schaefer (LS) film of traditional calamitic liquid crystal molecule, 4-octyl-4-biphenylcarbonitrile (8CB). The SAM of MUA was found to be non-responsive towards the change in resonance angle (RA) of surface plasmon resonance (SPR) due to the change in polarization of the external EM wave. However, such layer provides a soft-surface platform for the single layer of 8CB molecules which gets perturbed locally due to the incidence of the external EM wave. We obtained an oscillatory modulation of the change in RA due to the change in polarization angle of the EM wave with respect to the plane of incidence. The magnitude of sensitivity was found to be ∼4 milli°/° angle of polarization of the external EM wave. This study strongly suggests that sensitivity of a SPR-based sensor can be controlled by altering the linear state of polarization of the incident external EM wave.

Antimicrobial Active Bioplastics Using Triangular Silver Nanoplate Integrated Polycaprolactone and Polylactic Acid Films

An innovative antimicrobial technology for plastic surfaces is presented. We report the synthesis and scale-up of triangular silver nanoplates (TSNPs) and their integration into polycaprolactone (PCL) and polylactic acid (PLA) polymers through a solvent-casting technique. The TSNPs have a high geometric aspect ratio and strong local surface plasmon resonance (LSPR) response, which provides an effective tool for monitoring their integrity during processing and integration with the biodegradable plastics. An aqueous-based seed-mediated chemical method was used to synthesize the TSNPs, and characterisation was carried out using TEM and UV (Ultraviolet)-VIS (Visible) spectroscopy to measure LSPR profiles. The UV-VIS spectra of silver seeds and TSNPs exhibited characteristic peaks at 395 and 600 nm respectively. Synthesized TSNPs were coated with thiol-terminated polyethylene glycol (SH-PEG) and transferred into chloroform in order to effect compatibility with PCL and PLA. TSNP/PCL and TSNP/PLA composite films were prepared by solvent casting. The morphological structure, thermal, mechanical, and antimicrobial properties of the TSNP-incorporated composite films were evaluated. Results showed the TSNP-treated films had a rougher surface than the bare films. Insignificant changes in the thermal properties of TSNP-treated films compared to bare ones were also observed, which indicated the thermal stability of the composite films. The tensile strength and antimicrobial properties of the composite films were increased after TSNP incorporation. TSNP/PCL and TSNP/PLA films exhibited improved antimicrobial activity against Escherichia coli and Staphylococcus aureus with antimicrobial effect (AE) values ranging between 0.10 and 0.35. The obtained results and demonstrated TSNP production scalability validate the TSNP treated PCL and PLA films as a composite material with desirable antimicrobial effect for wide-ranging surface applications.

Real-Time Analysis of Polyphenol-Protein Interactions by Surface Plasmon Resonance Using Surface-Bound Polyphenols.

A selection of bioactive polyphenols of different structural classes, such as the ellagitannins vescalagin and vescalin, the flavanoids catechin, epicatechin, epigallocatechin gallate (EGCG), and procyanidin B2, and the stilbenoids resveratrol and piceatannol, were chemically modified to bear a biotin unit for enabling their immobilization on streptavidin-coated sensor chips. These sensor chips were used to evaluate in real time by surface plasmon resonance (SPR) the interactions of three different surface-bound polyphenolic ligands per sensor chip with various protein analytes, including human DNA topoisomerase IIα, flavonoid leucoanthocyanidin dioxygenase, B-cell lymphoma 2 apoptosis regulator protein, and bovine serum albumin. The types and levels of SPR responses unveiled major differences in the association, or lack thereof, and dissociation between a given protein analyte and different polyphenolic ligands. Thus, this multi-analysis SPR technique is a valuable methodology to rapidly screen and qualitatively compare various polyphenol-protein interactions.

Gold nanoparticles produced using NaBH4 in absence and in the presence of one-tail or two-tail cationic surfactants: Characteristics and optical responses induced by aminoglycosides

Gold nanoparticles (AuNPs), produced using sodium borohydride in water (AuNPs-H), also in the presence of the surfactants cetyltrimethylammonium bromide (AuNPs-CTAB) and didecyldimethylammonium bromide (AuNPs-D10AB), were characterized and investigated in terms of their optical localized surface plasmon resonance (LSPR) response. The automation of the syntheses improved reproducibility of AuNPs. CTAB was chosen as a model one-tail surfactant capping agent for AuNPs and D10AB (two-tail surfactant) was employed for the first time, as a capping agent for AuNPs. Thus, it was possible to carry out a comparative study for the production of AuNPs, varying the surfactant concentration levels from 1.0 × 10−2 to 1 × 10-4 mol L-1. The LSPR profiles were monitored in function of the time, taking into account storage conditions (at 4 °C and at 27 °C). A more unstable behavior was observed for the AuNPs produced in the presence of D10AB at 1.0 × 10-4 mol L-1, which suggested the disassembling of AuNPs over time. The catalytic activity of the AuNPs was evaluated in the presence of 4-nitrophenol, and the most effective kinetics were observed for systems containing the one-tail surfactant CTAB, at 1.0 × 10−2 mol L-1 (8 min), and for AuNPs-H, which has no organic coating, (6 min). Finally, the evaluation of the optical response from AuNPs was conducted with four aminoglycosides (AMG), indicating that these surfactants prevent interaction between AMG and the surface of the nanoparticles since at higher concentrations of CTAB or D10AB there is no significant variation in the LSPR spectral band in presence of AMG. In contrast, strong interaction, observed as variation of LSPR band, was found for the AuNPs-H-AMG systems.

Electron energy-loss spectroscopy of surface plasmon activity in wrinkled gold structures.

The surface plasmon response of a cross-sectional segment of a wrinkled gold film is studied using electron energy loss spectroscopy (EELS). EELS data demonstrate that wrinkled gold structures act as a suitable substrate for surface plasmons to propagate. The intense surface variations in these structures facilitate the resonance of a wide range of surface plasmons, leading to the broadband surface plasmon response of these geometries from the near-infrared to visible wavelengths. The metallic nanoparticle boundary element method toolbox is used to simulate plasmon eigenmodes in these structures. Eigenmode simulations show how the diverse morphology of the wrinkled structure leads to its high spectral complexity. Micron-sized structural features that do not provide interactions between segments of the wrinkle have only a small effect on the surface plasmon resonance response, whereas nanofeatures strongly affect the resonant modes of the geometry. According to eigenmode calculations, different eigenenergy shifts around the sharp folds contribute to the broadband response and infrared activity of these structures; these geometrical features also support higher energy (shorter wavelength) symmetric and anti-symmetric plasmon coupling across the two sides of the folds. It is also shown that additional plasmon eigenstates are introduced from hybridization of modes across nanogaps between structural features in close proximity to each other. All of these factors contribute to the broadband response of the wrinkled gold structures.

Real-time synthesis and detection of plasmonic metal (Au, Ag) nanoparticles under monochromatic X-ray nano-tomography

Plasmonic nanostructures are of immense interest of research due to its widespread applications in microelectronics, photonics, and biotechnology, because of its size and shape-dependent localized surface plasmon resonance response. The great efforts have been constructed by physicists, chemists, and material scientists to deliver optimized reaction protocol to tailor the size and shape of nanostructures. Real-time characterization emerges out as a versatile tool in perspective to the optimization of synthesis parameters. Moreover, in the past decades, radiation-induced reduction of metallic-salt to nanoparticles dominates over the conventional direct chemical reduction process which overcomes the production of secondary products and yields ultra-high quality and pure nanostructures. Here we show, the real-time/in-situ synthesis and detection of plasmonic (Au andAg) nanoparticles using single synchrotron monochromatic 6.7 keV X-rays based Nano-Tomography beamline. The real-time X-ray nano-tomography of plasmonic nanostructures has been first-time successfully achieved at such a low-energy that would be leading to the possibility of these experiments at laboratory-based sources. In-situ optical imaging confirms the radiolysis of water molecule resulting in the production of e_{aq}^-,,OH^bullet , and O_2^- under X-ray irradiation. The obtained particle-size and size-distribution by X-ray tomography are in good agreement to TEM results. The effect of different chemical environment media on the particle-size has also been studied. This work provides the protocol to precisely control the size of nanostructures and to synthesize the ultrahigh-purity grade monodisperse nanoparticles that would definitely enhance the phase-contrast in cancer bio-imaging and plasmonic photovoltaic application.

Light-triggered Janus nanomotor for targeting and photothermal lysis of pathogenic bacteria.

The rapid photothermal lysis of Escherichia coli O157:H7 treated with light-triggered Janus nanomotors was visualized by Hilbert differential contrast transmission electron microscopy (HDC-TEM). The extraordinary advantage of this high-resolution microscopic technique was that it revealed the detailed ultrastructure alterations of the treated cells at a state close to their native one. The micrographs demonstrated that Janus nanomotors (mesoporous silica nanoparticles with gold hemisphere and half-capped with cysteamine) were able to target and bind to the pathogenic E. coli. The biorecognition reaction proceeded at slightly acid pH thankful to the formed electrostatic adhesion between positively charged amino groups on nanoparticles surface and the negatively charged cell envelope. The exposure of labeled cells to near infrared laser irradiation leaded to occurrence of effective photothermal damage of their plasma membranes, which was enough strong to lyse bacteria. It was because of the overheating obtained by the photon-to-thermal conversion reaction generated by the surface plasmon resonance response of Janus nanomotors. The good efficiency of photothermal lysis to inactivate E. coli O157:H7 was confirmed by staining with LIVE/DEAD viability kit and quantification of the few survived cells in epifluorescence microscope. Furthermore, HDC-TEM images of ice-embedded inhibited bacteria documented the labeling, membrane disruptions and lysis due to the designed operation of Janus nanomotors. The reported microscopic technique provides a novel strategy for developing of Janus nanomachines as promising platform for nondrug treatment and defeating of antibiotic-resistant pathogenic microorganisms.

SmartSPR sensor: Machine learning approaches to create intelligent surface plasmon based sensors

Surface plasmon resonance (SPR) based sensors allow the evaluation of aqueous and gaseous solutions from real-time measurements of molecular interactions. The reliability of the response generated by a SPR sensor must be guaranteed, especially in substance detection, diagnoses, and other routine applications since poorly handled samples, instrumentation noise features, or even molecular tampering manipulations can lead to wrong interpretations. This work investigates the use of different machine learning (ML) techniques to deal with these issues, and aim to improve and attest to the quality of the real-time SPR responses so-called sensorgrams. A new strategy to describe a SPR-sensorgram is shown. The results of the proposed ML-approach allow the creation of intelligent SPR sensors to give a safe, reliable, and auditable analysis of sensorgram responses. Our arrangement can be embedded in an Intelligence Module that can classify sensorgrams and identify the substances presents in it. Also made it possible to order and analyze interest areas of sensorgrams, standardizing data, and supporting eventual audit procedures. With those intelligence features, the new generation of SPR-intelligent biosensors is qualifying to perform automated testing. A properly protocol for Leishmaniasis diagnosis with SPR was used to verify this new feature.

Label-Free Analysis with Multiple Parameters Separates G Protein-Coupled Receptor Signaling Pathways.

Real-time label-free techniques are used to profile G protein-coupled receptor (GPCR) signaling pathways in living cells. However, interpreting the label-free signal responses is challenging, and previously reported methods do not reliably separate pathways from each other. In this study, a continuous angular-scanning surface plasmon resonance (SPR) technique is utilized for measuring label-free GPCR signal profiles. We show how the continuous angular-scanning ability, measuring up to nine real-time label-free parameters simultaneously, results in more information-rich label-free signal profiles for different GPCR pathways, providing a more accurate pathway separation. For this, we measured real-time full-angular SPR response curves for Gs, Gq, and Gi signaling pathways in living cells. By selecting two of the most prominent label-free parameters: the full SPR curve angular and intensity shifts, we present how this analysis approach can separate each of the three signaling pathways in a straightforward single-step analysis setup, without concurrent use of signal inhibitors or other response modulating compounds.