Changes In Fluorescence Intensity Research Articles

The apoptosis of Chlorella vulgaris and the release of intracellular organic matter under metalimnetic oxygen minimum conditions

Metalimnetic oxygen minimum (MOM) is a frequent occurrence in lakes and reservoirs, and its formation is related to the blooming and apoptosis of algae. In this study, the apoptosis mechanism of Chlorella vulgaris (C. vulgaris) and the release of intracellular organic matter (IOM) under different MOM conditions were analyzed by changing the dissolved oxygen (DO) (7.0 mg/L, 3.0 mg/L, and 0.3 mg/L) and water pressure (0.3 MPa and normal pressure). The integrity and auto-fluorescence of algae cells decreased rapidly in the first 8 days, and then stabilized gradually during the development of MOM. Compared with that of water pressures, DO had a significant effect on the activity of algal cells, and higher initial DO levels (3.0 mg/L and 7.0 mg/L) accelerated the lysis of algal cells. The integrity of algae cells decreased to 28.8 %, 31.8 % and 56.6 % at the initial DO of 7 mg/L, 3 mg/L and 0.3 mg/L under 0.3 MPa, respectively. Meanwhile, the concentration of dissolved organic carbon (DOC) and dissolved organic nitrogen (DON) continued to increase and reached their maximum at 8 or 12 days, respectively, due to the IOM release caused by algal cell rupture, and then gradually decreased due to microbial degradation. Consistent with the results of membrane integrity, the highest DOC and DON concentrations were found at higher initial DO conditions. By parallel factor analysis, the change in total organic matter fluorescence intensity was consistent with DOC, once again increasing in the first 8 days and then gradually decreasing. The increased humic-like component, which is related to higher aromaticity, led to the monotonic increase of HAAFPs and THMFPs. However, the released IOM of C. vulgaris had lower N-DBPFPs, with TCNMFP predominating primarily. In summary, these results shed new lights on exploring the apoptosis of algae and the release of IOM during the development of MOM.

Carbon quantum dots as fluorescent probes in the measurement of the critical micelle concentration of surfactants

The critical micelle concentration (CMC) is one main parameter of surfactants, so an accurate, rapid, and convenient method for CMC determination is of great significance for surfactant applications. In this paper, three samples of carbon quantum dots (CQDs) with different fluorescence properties were developed as fluorescent probes for the CMC determination of CTAB, SDS, Triton X-100, perfluoro OBS and Pluronics® P-123. The fluorescence excitation and emission spectra of a constant amount of the CQDs in different concentrations of the surfactant solution were recorded, and then the CMC values of the surfactant were deduced from the fluorescence intensity change and the Stokes shift variation. The obtained CMC data using three samples of the CQDs agree well with those in the published literature. It is also demonstrated that in the micellization process the interaction between the CQDs and the surfactant molecules is complicated, because the fluorescence properties of the CQDs are found to be related to the characteristics of the CQDs, the head group type of ionic surfactants, the chemical structure between the hydrophobic and hydrophilic segment, and the chemical nature of the hydrophobic chains of the surfactants. So, the CQDs are demonstrated to be located at the palisade layer in the surfactant micelles due to the surface-attached polar groups on the CQDs although the CQDs are mainly hydrophobic as fluorescent probes. The fluorescent CQDs are considered to be new choices of the fluorescent probes in the facile CMC measurement of the surfactants.

Condensed tannin accretions specifically distributed in mesophyll cells of non-salt secretor mangroves help in salt tolerance.

Auto-fluorescent condensed tannins specifically accumulated in mesophyll cells of non-salt secretor mangroves are involved in the compartmentation of Na+ and osmotic regulation, contributing to their salt tolerance. Salinity is a major abiotic stress affecting the distribution and growth of mangrove plants.The salt exclusion mechanism from salt secretor mangrove leaves is quite known; however, salt management strategies in non-salt secretor leaves remain unclear. In this study, we reported the auto-fluorescent inclusions (AFIs) specifically accumulated in mesophyll cells (MCs) of four non-salt secretor mangroves but absent in three salt secretors. The AFIs increased with the leaf development under natural condition, and applied NaCl concentrations applied in the lab. The AFIs in MCs were isolated and identified as condensed tannin accretions (CTAs) using the dye dimethyl-amino-cinnamaldehyde (DMACA), specific for condensed tannin (CT), both in situ leaf cross sections and in the purified AFIs. Fluorescence microscopy and transmission electron microscope (TEM) analysis indicated that the CTAs originated from the inflated chloroplasts. The CTAs had an obviousmembrane and could induce changes in shape and fluorescence intensity in hypotonic and hypertonic NaCl solutions, suggesting CTAs might have osmotic regulation ability and play an important role in the osmotic regulation in MCs. The purified CTAs were labeled by the fluorescent sodium-binding benzofuran isophthalate acetoxymethyl ester (SBFI-AM), confirming they were involved in the compartmentation of excess Na+ in MCs. This study provided a new view on the salt resistance-associated strategies in mangroves.

Particle size and morphology-selective synthesis of mesoporous silica and study of its interaction with human serum albumin: spherical versus rod-like shape

Mesoporous silica (MS) has gained considerable attention as a promising material for biomedical applications. The morphology of MS can affect its interaction with biomacromolecules, leading to changes in their biological performance. Herein, we aim to study human serum albumin (HSA) binding to spherical MS (SMS) versus rod-like MS (RMS). For this purpose, the Stöber method is exploited and the impact of synthesis variables on the MS morphology and size is examined. Next, the binding of SMS versus RMS with HSA is evaluated using fluorescence spectroscopy. The intrinsic fluorescence intensity changes show the combined dynamic and static quenching mechanism with the dominant contribution of the static mode in the MSs interaction with HSA. However, the RMS-HSA complex is more stable, with a binding constant of 0.03 × 106 M−1 at 37 °C compared to the SMS-HAS complex. The hydrophobic interaction is the driving force for SMS and RMS binding to HSA.

Neodymium and manganese ions co-doped whitlockite for temperature monitoring, photothermal therapy, and bone tissue repair in osteosarcoma

Osteosarcoma is one of the most dangerous forms of tumors, leading to death in >90% of patients. The surgical treatment of osteosarcoma results in significant bone defects and risks of tumor recurrence. Using neodymium (Nd) and manganese (Mn) ions co-doped with whitlockite nanoparticle (Nd10%Mn10%WH NPs) and sodium alginate (SA), we designed and synthesized an organic–inorganic composite hydrogel (Nd10%Mn10%WH-SA) that displayed the excellent fluorescence and photothermal properties. Furthermore, the maximum fluorescence emission intensity of Nd10%Mn10%WH-SA at 1062 nm was linear with temperature. The optimal temperature for the treatment of tumors was determined by considering the changes in fluorescence intensity that led to a reduction in tissue damage around the tumors. Nd10%Mn10%WH NPs demonstrated a significant function in promoting human bone marrow mesenchymal stem cells (hBMSCs) proliferation. Furthermore, Nd10%Mn10%WH-SA could almost kill tumors when the photothermal temperature was raised to 50 °C, with a minimal leftover scar after photothermal therapy (PTT). Nd10%Mn10%WH-SA had a better promotion effect on the growth of the new bone. These results suggested that Nd10%Mn10%WH-SA offers a new PTT method for the “integrated treatment and repair” of osteosarcoma.

Electrostatic-Mediated Binding of DNA to Lysozymes: Evaluation of Aptamer-Based Assays for Highly Positively Charged Targets.

Lysozymes are a highly popular protein target for the development of aptamer-based biosensors. Because a lysozyme is a polycation and DNA is a polyanion, it is essential to separate the contribution of nonspecific electrostatic interactions from specific aptamer binding. In this study, various factors affecting the binding of DNA and lysozymes, including the DNA sequence, DNA length, pH, and salt concentration, were explored using fluorescence polarization. We concluded that direct fluorescence polarization and fluorescence intensity changes are unlikely to be directly applicable for aptamer-based biosensors to detect lysozymes because all of the tested DNA sequences showed binding. These fundamental studies confirm the dominant role of electrostatic binding. We further evaluated three other methods, including label-free fluorescent detection using a DNA staining dye, label-free colorimetric detection using gold nanoparticles, and a fluorescent sensor based on the strand displacement reaction. In each case, we focused on a random DNA sequence that is not expected to bind to the lysozyme as an aptamer. Of all the methods, only the strand displacement strategy can be potentially used to evaluate aptamer binding, as the other methods all responded to nonaptamer sequences. This study provides valuable insights for assaying aptamer binding to cationic proteins that can exhibit a nonspecific attraction to DNA.

Dual-mode immunochromatographic assay based on dendritic gold nanoparticles with superior fluorescence quenching for ultrasensitive detection of E. coli O157:H7.

We presented a colorimetric/fluorescent dual-mode immunochromatographic assay (ICA) for the sensitive detection of Escherichia coli O157:H7. The use of polydopamine (PDA)-modified gold nanoparticles (AuNPs) with broadband absorption allowed for excellent colorimetry signals for the ICA detection. Moreover, the absorption spectrum of PDA-AuNPs significantly overlaps with the excitation and emission spectra of ZnCdSe/ZnS quantum dots (QDs), resulting in effective quenching of the QDs fluorescence due to the inner filter effect. The fluorescence intensity changes induced by PDA-AuNPs were utilized for the sensitive detection of E. coli O157:H7, achieving a detection limit of 9.06×101 CFU/mL, which was 46-fold lower than that of traditional AuNPs-based immunoassay. The proposed immunosensor exhibited the recovery rate between 80.12% and 114.69% in detecting actual samples, indicating its reliability and satisfactory accuracy. This study provides insights into dual-mode signal outputs and the ICA development for food safety applications.

Dual-Mode Gold Nanocluster-Based Nanoprobe Platform for Two-Photon Fluorescence Imaging and Fluorescence Lifetime Imaging of Intracellular Endogenous miRNA.

Bioimaging is widely used in various fields of modern medicine. Fluorescence imaging has the advantages of high sensitivity, high selectivity, noninvasiveness, in situ imaging, and so on. However, one-photon (OP) fluorescence imaging has problems, such as low tissue penetration depth and low spatiotemporal resolution. These disadvantages can be solved by two-photon (TP) fluorescence imaging. However, TP imaging still uses fluorescence intensity as a signal. The complexity of organisms will inevitably affect the change of fluorescence intensity, cause false-positive signals, and affect the accuracy of the results obtained. Fluorescence lifetime imaging (FLIM) is different from other kinds of fluorescence imaging, which is an intrinsic property of the material and independent of the material concentration and fluorescence intensity. FLIM can effectively avoid the fluctuation of TP imaging based on fluorescence intensity and the interference of autofluorescence. Therefore, based on silica-coated gold nanoclusters (AuNCs@SiO2) combined with nucleic acid probes, the dual-mode nanoprobe platform was constructed for TP and FLIM imaging of intracellular endogenous miRNA-21 for the first time. First, the dual-mode nanoprobe used a dual fluorescence quencher of BHQ2 and graphene oxide (GO), which has a high signal-to-noise ratio and anti-interference. Second, the dual-mode nanoprobe can detect miR-21 with high sensitivity and selectivity in vitro, with a detection limit of 0.91 nM. Finally, the dual-mode nanoprobes performed satisfactory TP fluorescence imaging (330.0 μm penetration depth) and FLIM (τave = 50.0 ns) of endogenous miR-21 in living cells and tissues. The dual-mode platforms have promising applications in miRNA-based early detection and therapy and hold much promise for improving clinical efficacy.

Monitoring and kinetic study of alkaline hydrolysis of polylactic acid fibrous membrane via aggregation-induced emission (AIE) technique

Hydrolysis mechanism of polylactic acid (PLA) materials has been the focus of PLA material research. Herein, we report a novel method for monitoring the hydrolysis of PLA. Tetraphenylene aldehyde (TPEA) with aggregation induced emission (AIE) property was synthesized as a fluorescence probe for being introduced into PLA-base fibrous membrane via electrospinning. Then, the obtained TPEA/PLA composite fibrous membrane was hydrolyzed in an aqueous environment with controllable temperature and pH. The detection of PLA hydrolysis was achieved by examining the fluorescence intensity changes caused by the release of TPEA during the hydrolysis. On the basis of the structure study of the prepared fibrous membranes, this study investigated the changes in fluorescence intensity of the degradation environment during the hydrolysis process. The correlation between fluorescence and PLA hydrolysis was investigated with the kinetic research to prove the feasibility of monitoring PLA hydrolysis via AIE technique.

Naphthyridine-based neutral fluorescent probes for dynamic monitoring lipid droplet polarity

In this paper, several novel nitrogen-containing heterocycle dyes 1a-c with large conjugated planar structures based on naphthyridine derivatives were designed and synthesized, which had excellent optical properties and biological applications. Optical test showed the maximum absorption wavelengths of 1a-c were in the range of 443–485 nm, while the maximum emission wavelengths located at 523–610 nm in difference solvents. Furthermore, they exhibited polarity related fluorescence intensity changes with high fluorescence quantum yields, even up to 88% (1a in THF). Moreover, the transient absorption spectra revealed the excited-state lifetime of dye 1a became shorter with the increase of solvent polarity. Density functional theory calculations are also used to help explain the effect of the polarity of solvents on their fluorescence properties. Interestingly, the dyes 1a-c were somewhat toxic to cancer cells, while had an obvious growth-promoting effect on normal cells. Additionally, 1a-c with excellent lipid droplet (LD) targeting could be used for long-term observation of targeted cellular lis) hysiological activity and further applied to dynamic monitoring of changes in LDs polarity stimulated by TLR4 activator (LPS) in living cells. Overall, the excellent optical properties and biocompatibility of 1a-c indicate that they can serve as fluorescent probes for biological applications, and the results have important implications for understanding the physiological functions of LDs, especially in terms of morphological and polar changes.

A self-monitoring microneedle patch for light-controlled synergistic treatment of melanoma.

Melanoma is the most aggressive and malignant form of skin cancer. Current melanoma treatment methods generally suffer from frequent drug administration as well as difficulty in direct monitoring of drug release. Here, a self-monitoring microneedle (MN)-based drug delivery system, which integrates a dissolving MN patch with aggregation-induced emission (AIE)-active PATC microparticles, is designed to achieve light-controlled pulsatile chemo-photothermal synergistic therapy of melanoma. The PATC polymeric particles, termed D/I@PATC, encapsulate both of chemotherapeutic drug doxorubicin (DOX) and the photothermal agent indocyanine green (ICG). Upon light illumination, PATC gradually dissociates into smaller particles, causing the release of encapsulated DOX and subsequent fluorescence intensity change of PATC particles, thereby not only enabling direct observation of the drug release process under light stimuli, but also facilitating verification of drug release by fluorescence recovery after light trigger. Moreover, encapsulation of ICG in PATC particles displays significant improvement of its photothermal stability both in vitro and in vivo. In a tumor-bearing mouse, the application of one D/I@PATC MN patch combining with two cycles of light irradiation showed excellent controllable chemo-photothermal efficacy and exhibited ∼97% melanoma inhibition rate without inducing any evident systemic toxicity, suggesting a great potential for skin cancer treatment in clinics.

Experimental Verification of the Accuracy of Oxygen-Varying Correlated Fluorescence for Determining the Quenching Constant KSV.

The oxygen-varying correlated fluorescence provides an effective strategy to gain the quenching constant KSV for a non-phosphorescent system. Owing to the absence of detectable phosphorescence emission in general optical spectroscopy, the facticity of this method has never been verified. Here, the correct way to determine KSV by oxygen-varying correlated fluorescence was systematically studied in detail. We selected gadolinium protoporphyrin IX (Gd-PpIX) to establish a fluorescence and phosphorescence dual emission system. Then, KSV of Gd-PpIX can be obtained by the change of fluorescence intensity (IF) with oxygen concentration using the method of correlated fluorescence at intense pump power; meanwhile, the value can also be determined from the relationship of the phosphorescence intensity ratio and oxygen content by the Stern-Volmer equation under relatively low power density. It was found that the KSV values obtained by the above two methods were 12.2(1) and 11.9(7) kPa-1, respectively. Our results successfully verified the accuracy of oxygen-varying correlated fluorescence for determining the KSV by the phosphorescence property and fluorescence saturation of Gd-PpIX.

Single Walled Carbon Nanotube (SWCNT) Detection of Interleukin 1 β (IL-1β)

Single walled carbon nanotubes (SWCNTs) are known for their fluorescent properties in the near-infrared region, as well as their photostability and emission within the “biological transparency window”. This makes them useful as nanosensors for in vivo signal detection. The stability of SWCNTs also allows for repeated, long-term measurements. Implantation of these sensors in vivo allow for detection of biomarkers of specific diseases. Interleukin 1 β (IL-1β) is a pro-inflammatory cytokine involved in pleiotropic cellular processes. IL-1β is commonly found at elevated levels in cancerous tissues and other chronic diseases. We are working to design an IL-1β nanosensor by evaluation of optical band gap changes in the presence of the desired antigen. This is accomplished by conjugating an antibody of interest to the SWCNT wrapped with TAT6-NH2 DNA oligonucleotide and passivating the surface of the SWCNT with bovine serum albumin (BSA). This causes the SWCNT’s hydrophobic surface to be less available for non-specific protein interference, creating a more functional sensor. We observed significant changes in the sensor’s center wavelength and change in fluorescence intensity in the antigen’s presence, serving as an indication of the functionality of the nanosensor. We are also working on studying the capability of fluorescent dyes to exacerbate the wavelength shift seen in SWCNTs. This is accomplished by conjugating the dye to a nanosensor and introducing its complimentary antigen that will remove the dye from the SWCNT surface, intensifying its shift in wavelength. The overall goal of developing this type of nanosensor is to use it in point-of-care scenarios to measure biomarker levels in patient samples or in vivo, allowing for detection of chronic diseases that may be difficult to diagnose early on.

Investigation of variation in fluorescence intensity from rhodamine 6G dye in a trapped and levitated liquid micro-drop

Variation in fluorescence intensity from rhodamine 6 G dye was investigated. A small volume of dye solution, in the form of a trapped and levitated micro-drop, was optically excited with a 400 μW, 532 nm wavelength cw-laser light. The dye was dissolved in methanol and glycerol for a concentration of 10 mg/ml or 21 mMole per liter. With the optical excitation, initially the fluorescence intensity was observed to rise with time, and then it decayed, along with a steady shift of fluorescence peak from 562 nm to 543 nm. The observation of initial enhancement in fluorescence from start to 7 min of excitation, can partly be due to the low excitation power, less dimer formation and gradual rise in molecular population to excited state therefore slower rate of change (increase) of fluorescence intensity was observed with time. Simulation studies indicate that the photo bleaching was taking place from all the energy states of the dye molecules, which is an extension of the concept that the photo bleaching takes place at the excited triplet state whereas the fluorescence takes place due to transition between excited singlet states and ground states. A steady shift in fluorescence peak position, from 562 nm to 543 nm, was observed during the fluorescence life of the dye, at a rate of 0.0113 nm/s during fluorescence enhancement and 0.026 nm/s during photo-bleaching. The steady blue shift of fluorescence indicate insignificant dimer formation.

A Polarity-Sensitive Far-Red Fluorescent Probe for Glucose Sensing through Skin.

The field of glucose biosensors for diabetes management has been of great interest over the past 60 years. Continuous glucose monitoring (CGM) is important to continuously track the glucose level to provide better management of the disease. Concanavalin A (ConA) can reversibly bind to glucose and mannose molecules and form a glucose biosensor via competitive binding. Here, we developed a glucose biosensor using ConA and a fluorescent probe, which generated a fluorescent intensity change based on solvatochromism, the reversible change in the emission spectrum dependent on the polarity of the solvent. The direction in which the wavelength shifts as the solvent polarity increases can be defined as positive (red-shift), negative (blue-shift), or a combination of the two, referred to as reverse. To translate this biosensor to a subcutaneously implanted format, Cyanine 5.5 (Cy5.5)-labeled small mannose molecules were used, which allows for the far-red excitation wavelength range to increase the skin penetration depth of the light source and returned emission. Three Cy5.5-labeled small mannose molecules were synthesized and compared when used as the competing ligand in the competitive binding biosensor. We explored the polarity-sensitive nature of the competing ligands and examined the biosensor's glucose response. Cy5.5-mannotetraose performed best as a biosensor, allowing for the detection of glucose from 25 to 400 mg/dL. Thus, this assay is responsive to glucose within the physiologic range when its concentration is increased to levels needed for an implantable design. The biosensor response is not statistically different when placed under different skin pigmentations when comparing the percent increase in fluorescence intensity. This shows the ability of the biosensor to produce a repeatable signal across the physiologic range for subcutaneous glucose monitoring under various skin tones.

Low-Cost Full-Range Detection of C-Reactive Protein in Clinical Samples by Aptamer Hairpin Probes and Coprecipitation of Silver Ions and Gold Nanoparticles.

C-reactive protein (CRP) levels can vary widely related to diverse disease contexts. However, expensive antibodies have impeded the clinical utility of antibody-based full-range CRP assays, especially in developing countries. Herein, we established a low-cost, antibody-free, 96-well plate-based full-range CRP detection method by combining gold nanoparticles (AuNPs), silver iodide (AgI), Eosin Y, and the aptamer hairpin probe (AHP) with Ag+-mediated cytosine-cytosine mismatches, that is, the Au@AgI/Eosin Y-AHP method. After binding the target CRP, the AHP released Ag+, which subsequently induced the aggregation of AuNPs on the surface of AgI colloids, resulting in a significant increase in the adsorption of Eosin Y on the surface of AuNPs. The changes in fluorescence intensity (FI) of Eosin Y in the supernate without and with CRP were proportional to the concentration of the CRP in the wide range of 0.01-40 ng/mL (r = 0.9969), and 96 samples can be detected in 96-well plates simultaneously by a microplate reader within 45 min. Remarkably, the CRP levels of 100 clinical samples achieved with the Au@AgI/Eosin Y-AHP had a good correlation with those obtained with the latex-enhanced immune turbidimetry assay (r = 0.986). Furthermore, the kit based on the Au@AgI/Eosin Y-AHP method costs only $8.1 for 100 tests. Therefore, the new method is beneficial for less developed areas where expensive assays are not affordable.

Homogeneous Dual Fluorescence Count of CD4 in Clinical HIV-Positive Samples via Parallel Catalytic Hairpin Assembly and Multiple Recognitions.

Regularly measuring the level of CD4+ cells is necessary for monitoring progression and predicting prognosis in patients suffering from an infection with the human immunodeficiency virus (HIV). However, the current flow cytometry standard detection method is expensive and complicated. A parallel catalytic hairpin assembly (CHA)-assisted fluorescent aptasensor is reported for homogeneous CD4 count by targeting the CD4 protein expressed on the membrane of CD4+ cells. Detection was achieved using CdTe quantum dots (QDs) and methylene blue (MB) as signal reporters. CdTe QDs distinguished CHA-assisted release of Ag+ and C-Ag+-C and MB that has differentiated cytosine (C)-rich single-stranded DNA (ssDNA) and C-Ag+-C, generating changes in fluorescence intensity. With the assistance of the CHA strategy and luminescent nanomaterials, this method reached limits of detection of 0.03 fg/mL for the CD4 protein and 0.3 cells/mL for CD4+ cells with linear ranges of 0.1 to 100 fg/mL and 1 to 1000 cells/mL, respectively. The method was validated in 50 clinical whole blood samples consisting of 30 HIV-positive patients, 10 healthy volunteers, and 10 patients with cancer or other chronic infections. The findings from this method were in good agreement with the data from clinical flow cytometry. Due to its sensitivity, affordability, and ease of operation, the current method has demonstrated great potential for routine CD4 counts for the management of HIV, especially in communities and remote areas.

LUMINESCENT PROPERTIES OF Nd(III) COMPLEXES WITH ETHY­LENE­DIAMINE-N,N'-DISUCCINIC AND N,N-BIS(PHOSPHONO­METHYL)-2-AMINOPROPIONIC ACIDS

An analysis of the fluorescent characteristics of ethylenediamine-N,N'-disuccinic and N,N-bis(phosphonomethyl)-2-aminopropionic acids was carried out depending on the pH of the solutions. It was established that the change in fluorescence intensity and lifetime is associated with the formation of variously protonated forms of acids in which stable H-cycles are formed with the participation of hydrogen bonds. The energies of the singlet and triplet levels of the ligands were experimentally determined, the values of which are higher than the energy of the radiative level of the Nd(III) ion, which indicates the possibility of intramolecular transfer of the excitation energy to the resonance level of the lanthanide ion. It was established that both homo- and heteronuclear complexes of Nd(III) exhibit 4f-luminescence in the near-IR region. It was found that for phosphorus-containing complexes there is an increase in luminescence intensity and relative quantum yields in comparison with aminocarboxylate analogs. In heterometallic complexes based on aminopolycarboxylic acids, the intramolecular transfer of energy from the excited level of Co(II) to the resonance level of the f-metal leads to sensitization of the 4f-luminescence of the neodymium ion.

Colorimetric and fluorescent dual-mode pH sensor with PMIA as substrate and CQDs as probe for high accuracy detection of full range pH

The pH test is particularly important in many fields, such as chemical production and medical diagnosis. However, the most commonly used pH test strips for pH detection have disadvantages such as low strength, poor stability, only qualitative measurement and only a single-color response. Therefore, a dual-mode pH sensor prepared by a phase conversion method with Poly(m-phenylene isophthalamide) (PMIA) as the substrate and carbon quantum dots (CQDs) as probes was developed. This sensor is capable of producing dual changes in fluorescence color and fluorescence intensity over the full range of pH. The -COOH and -NH2 groups in CQDs can interact with the amide group in PMIA to make the sensor highly stable. Three correlations were established based on the fluorescence color and fluorescence intensity at different pH, which compensated the shortage of traditional pH test paper that could not be quantitatively detected. More importantly, the sensor can be used for pH detection in a wide range of water samples, and both colorimetric and fluorescence detection modes exhibit extremely high fit coefficients (R2 > 0.99) and short response times (∼5 s). Therefore, the dual-mode pH sensor provides an important solution for the development of pH detection devices with high stability and accuracy.

Initiation and accumulation of loading induced changes to native collagen content and microstructural damage in the cartilaginous endplate

BACKGROUND CONTEXTInjury to the cartilaginous endplate (CEP) is linked to clinically relevant low back disorders, including intervertebral disc degeneration and pain reporting. Despite this link to clinical disorders, the CEP injury pathways and the modulating effect of mechanical loading parameters on the pace of damage accumulation remains poorly understood. PURPOSEThis study examined the effect of cyclic loading on the initiation and accumulation of changes to native collagen content (type I, type II) and microstructural damage in the central region of cadaveric porcine CEPs. STUDY DESIGNIn vitro longitudinal study. METHODSOne hundred fourteen porcine cervical spinal units were included (N=6 per group). The study contained a control group (no cyclic loading) and 18 experimental groups that differed by loading duration (1,000, 3,000, 5,000 cycles), joint posture (flexed, neutral), and cyclic peak compression variation (10%, 20%, 40%). Multicolor immunofluorescence staining was used to quantify loading induced changes to type I (ie, subchondral bone) and type II (ie, endplate) native collagen content (fluorescence area, fluorescence intensity) and microstructural damage (pore area [transverse plane], void area along the CEP-bone border [sagittal plane]). RESULTSSignificant main effects of loading duration and posture were observed for fluorescence area and fluorescence intensity of type I and II collagen. In the transverse plane, type II fluorescence area significantly decreased following 1,000 cycles (-12%), but a significant change in fluorescence intensity was not observed until 3,000 cycles (-17%). Type II fluorescence area (-14%) and intensity (-10%) were both significantly less in flexed postures compared to neutral. Similar trends were observed for type I collagen in the sagittal plane sections. Generally, significant changes to fluorescence area were accompanied by the development of microstructural voids along the endplate-subchondral bone border. CONCLUSIONSThese findings demonstrate that microstructural damage beneath the endplate surface occurs before significant changes to the density of native type I and II collagen fibers. Although flexed postures were associated with greater and accelerated changes to native collagen content, the injury initiation mechanism appears similar to neutral. CLINICAL SIGNIFICANCENeutral joint postures can delay the initiation and pace of microdamage accumulation in the CEP during low-to-moderate demand lifting tasks. Furthermore, the management of peak compression exposures appeared relevant only when a neutral posture was maintained. Therefore, clinical low back injury prevention and load management efforts should consider low back posture in parallel with applied joint forces.