Ultrasensitive surface-enhanced Raman scattering detection of trypsin based on anti-aggregation of 4-mercaptopyridine-functionalized silver nanoparticles: an optical sensing platform toward proteases

In this work, a simple and sensitive surface-enhanced Raman scattering (SERS) strategy was developed for recognition and detection of trypsin, by using anti-aggregation of 4-mercaptopyridine (4-MPY)-functionalized silver nanoparticles (AgNPs) based on the interaction between protamine and trypsin. The polycationic protamine not only served as a substrate for enzyme hydrolysis but also worked as a medium for SERS enhancement, which could bind negatively charged 4-MPY-functionalized AgNPs and induce their aggregation. The hydrolysis catalyzed with trypsin in sample solution decreased the concentration of free protamine, resulting in the dispersion of AgNPs and thus decreasing the Raman intensity of 4-MPY, by which the trypsin could be sensed optically. A detection level down to 0.1 ng mL(-1) for trypsin was obtained. The induced accumulation of AgNPs modified with Raman reporter 4-MPY largely enhanced the SERS responses. A good linearity was found within the wide range over five orders of magnitude and reasonable relative standard deviations (between 2.4 and 11.6%) were attained. By using trypsin as a model, the new concept can provide an excellent platform for ultrasensitive SERS measurements of various proteases/enzymes which can lead to nanoparticles stability change through catalyzed hydrolysis toward substrate.In this work, a simple and sensitive surface-enhanced Raman scattering (SERS) strategy was developed for recognition and detection of trypsin, by using anti-aggregation of 4-mercaptopyridine (4-MPY)-functionalized silver nanoparticles (AgNPs) based on the interaction between protamine and trypsin. The polycationic protamine not only served as a substrate for enzyme hydrolysis but also worked as a medium for SERS enhancement, which could bind negatively charged 4-MPY-functionalized AgNPs and induce their aggregation. The hydrolysis catalyzed with trypsin in sample solution decreased the concentration of free protamine, resulting in the dispersion of AgNPs and thus decreasing the Raman intensity of 4-MPY, by which the trypsin could be sensed optically. A detection level down to 0.1 ng mL(-1) for trypsin was obtained. The induced accumulation of AgNPs modified with Raman reporter 4-MPY largely enhanced the SERS responses. A good linearity was found within the wide range over five orders of magnitude and reasonable relative standard deviations (between 2.4 and 11.6%) were attained. By using trypsin as a model, the new concept can provide an excellent platform for ultrasensitive SERS measurements of various proteases/enzymes which can lead to nanoparticles stability change through catalyzed hydrolysis toward substrate

Fluorescent probes for hydrogen sulfide detection and bioimaging

In comparison with other biological detection technologies, fluorescence bioimaging technology has become a powerful supporting tool for intracellular detection, and can provide attractive facilities for investigating physiological and pathological processes of interest with high spatial and temporal resolution, less invasiveness, and a rapid response. Due to the versatile roles of hydrogen sulfide (H2S) in cellular signal transduction and intracellular redox status regulation, fluorescent probes for the detection of this third signalling gasotransmitter have rapidly increased in number in recent years. These probes can offer powerful means to investigate the physiological actions of H2S in its native environments without disturbing its endogenous distribution. In this feature article, we address the synthesis and design strategies for the development of fluorescent probes for H2S based on the reaction type between H2S and the probes. Moreover, we also highlight fluorescent probes for other reactive sulfur species, such as sulfane sulfurs and SO2 derivatives.In comparison with other biological detection technologies, fluorescence bioimaging technology has become a powerful supporting tool for intracellular detection, and can provide attractive facilities for investigating physiological and pathological processes of interest with high spatial and temporal resolution, less invasiveness, and a rapid response. Due to the versatile roles of hydrogen sulfide (H2S) in cellular signal transduction and intracellular redox status regulation, fluorescent probes for the detection of this third signalling gasotransmitter have rapidly increased in number in recent years. These probes can offer powerful means to investigate the physiological actions of H2S in its native environments without disturbing its endogenous distribution. In this feature article, we address the synthesis and design strategies for the development of fluorescent probes for H2S based on the reaction type between H2S and the probes. Moreover, we also highlight fluorescent probes for other reactive sulfur species, such as sulfane sulfurs and SO2 derivatives

Fluorescent and magnetic dual-responsive coreshell imprinting microspheres strategy for recognition and detection of phycocyanin

Molecular imprinting as a versatile technology is emerging for diverse species in various fields; however protein imprinting faces several problems related to the size, structural complexity, conformational flexibility, and compatibility with solvents. Herein, by using phycocyanin as a model, with physiological significance and fluorescence characteristics, we developed a facile and highly efficient approach to obtain fluorescent and magnetic dual-responsive coreshell imprinting microspheres. Twostage miniemulsion polymerization was employed, based on surface immobilization of phycocyanin with aminolysis and aldehyde modification on superparamagnetic support particles. The dual-responsive imprinting microspheres exhibited high adsorption capacity of 10.53 mg g(-1), excellent binding selectivity toward phycocyanin with a high imprinting factor of 2.41, and good reproducibility with standard error within 10%. Furthermore, fast simple magnetic separation and sensitive fluorescent detection in a wide pH range was offered for phycocyanin, showing a good linearity within 0.01-1.0 mg L-1 (R-2 = 0.9970) and a favorable detectability up to 1.5 ng mL(-1). Consequently, the imprinting microspheres were successfully applied as sorbents for selective isolation of phycocyanin from protein mixtures and special imaging recognition. Taking advantages of dual-responsive polymers and surface imprinting, the developed strategy provides great application potentials for convenient, rapid targeting identification/enrichment and separation of proteins and thereby contributing to targeting drug delivery and protein research.Molecular imprinting as a versatile technology is emerging for diverse species in various fields; however protein imprinting faces several problems related to the size, structural complexity, conformational flexibility, and compatibility with solvents. Herein, by using phycocyanin as a model, with physiological significance and fluorescence characteristics, we developed a facile and highly efficient approach to obtain fluorescent and magnetic dual-responsive coreshell imprinting microspheres. Twostage miniemulsion polymerization was employed, based on surface immobilization of phycocyanin with aminolysis and aldehyde modification on superparamagnetic support particles. The dual-responsive imprinting microspheres exhibited high adsorption capacity of 10.53 mg g(-1), excellent binding selectivity toward phycocyanin with a high imprinting factor of 2.41, and good reproducibility with standard error within 10%. Furthermore, fast simple magnetic separation and sensitive fluorescent detection in a wide pH range was offered for phycocyanin, showing a good linearity within 0.01-1.0 mg L-1 (R-2 = 0.9970) and a favorable detectability up to 1.5 ng mL(-1). Consequently, the imprinting microspheres were successfully applied as sorbents for selective isolation of phycocyanin from protein mixtures and special imaging recognition. Taking advantages of dual-responsive polymers and surface imprinting, the developed strategy provides great application potentials for convenient, rapid targeting identification/enrichment and separation of proteins and thereby contributing to targeting drug delivery and protein research

A highly sensitive colorimetric metalloimmunoassay based on copper-mediated etching of gold nanorods

A highly sensitive colorimetric metalloimmunoassay with a detection limit of 0.15 ng ml(-1) for human IgG based on coppermediated etching of gold nanorods was proposed. The assay is more sensitive than traditional ELISA, electrochemical metalloimmunoassay and HRP mimic nanomaterial tag-based immunoassay

Dual cloud point extraction coupled with hydrodynamic-electrokinetic two-step injection followed by micellar electrokinetic chromatography for simultaneous determination of trace phenolic estrogens in water samples

A dual cloud point extraction (dCPE) off-line enrichment procedure coupled with a hydrodynamic-electrokinetic two-step injection online enrichment technique was successfully developed for simultaneous preconcentration of trace phenolic estrogens (hexestrol, dienestrol, and diethylstilbestrol) in water samples followed by micellar electrokinetic chromatography (MEKC) analysis. Several parameters affecting the extraction and online injection conditions were optimized. Under optimal dCPE-two-step injection-MEKC conditions, detection limits of 7.9-8.9 ng/mL and good linearity in the range from 0.05 to 5 mu g/mL with correlation coefficients R (2) a parts per thousand yenaEuro parts per thousand 0.9990 were achieved. Satisfactory recoveries ranging from 83 to 108 % were obtained with lake and tap water spiked at 0.1 and 0.5 mu g/mL, respectively, with relative standard deviations (n = 6) of 1.3-3.1 %. This method was demonstrated to be convenient, rapid, cost-effective, and environmentally benign, and could be used as an alternative to existing methods for analyzing trace residues of phenolic estrogens in water samples.A dual cloud point extraction (dCPE) off-line enrichment procedure coupled with a hydrodynamic-electrokinetic two-step injection online enrichment technique was successfully developed for simultaneous preconcentration of trace phenolic estrogens (hexestrol, dienestrol, and diethylstilbestrol) in water samples followed by micellar electrokinetic chromatography (MEKC) analysis. Several parameters affecting the extraction and online injection conditions were optimized. Under optimal dCPE-two-step injection-MEKC conditions, detection limits of 7.9-8.9 ng/mL and good linearity in the range from 0.05 to 5 mu g/mL with correlation coefficients R (2) a parts per thousand yenaEuro parts per thousand 0.9990 were achieved. Satisfactory recoveries ranging from 83 to 108 % were obtained with lake and tap water spiked at 0.1 and 0.5 mu g/mL, respectively, with relative standard deviations (n = 6) of 1.3-3.1 %. This method was demonstrated to be convenient, rapid, cost-effective, and environmentally benign, and could be used as an alternative to existing methods for analyzing trace residues of phenolic estrogens in water samples

Ultrasensitive Visual Sensing of Molybdate Based on Enzymatic-like Etching of Gold Nanorods

Here, we have developed a novel approach to the visual detection of molybdate with high sensitivity and selectivity in aqueous media based on the combination of catalytic formation of iodine and iodine-mediated etching of gold nanorods. In weak acid solution, like peroxidase, molybdate can catalyze the reaction between H2O2 and I- to produce I-2, a moderate oxidant, which then etches gold nanorods preferentially along the longitudinal direction in the presence of hexadecyltrimethylammonium bromide. The etching results in the longitudinal localized surface plasmon resonance extinction peak shifts to short wavelength, accompanied by a color change from blue to red. Under optimal conditions, this sensor exhibits good sensitivity with a detection limit of 1.0 nM. The approach is highlighted by its high selectivity and tolerance to interference, which enables the sensor to detect molybdate directly in real samples, such as tap water, drinking water, and seawater. In addition, perhaps the proposed sensing strategy can be also used for other targets that can selectively regulate the formation of I-2 under given conditions

A molecular imprinting-based turn-on Ratiometric fluorescence sensor for highly selective and sensitive detection of 2,4-dichlorophenoxyacetic acid (2,4-D)

A novel molecular imprinting-based turn-on ratiometric fluorescence sensor was constructed via a facile sol-gel polymerization for detection of 2,4-dichlorophenoxyacetic acid (2,4-D) on the basis of photo induced electron transfer (PET) by using nitrobenzoxadiazole (NBD) as detection signal source and quantum dots (QDs) as reference signal source. With the presence and increase of 2,4-D, the amine groups on the surface of QDs@SiO2 could bind with 2,4-D and thereby the NBD fluorescence intensities could be significantly enhanced since the PET process was inhibited, while the QDs maintained constant intensities. Accordingly, the ratio of the dual-emission intensities of green NBD and red QDs could be utilized for turn-on fluorescent detection of 2,4-D, along with continuous color changes from orange-red to green readily observed by the naked eye. The as-prepared fluorescence sensor obtained high sensitivity with a low detection limit of 0.14 mu M within 5 min, and distinguished recognition selectivity for 2,4-D over its analogs. Moreover, the sensor was successfully applied to determine 2,4-D in real water samples, and high recoveries at three spiking levels of 2,4-D ranged from 95.0% to 110.1% with precisions below 4.5%. The simple, rapid and reliable visual sensing strategy would not only provide potential applications for high selective ultratrace analysis of complicated matrices, but also greatly enrich the research connotations of molecularly imprinted sensors. (C) 2016 Elsevier B.V. All rights reserved

Magnetic molecularly imprinted microsensor for selective recognition and transport of fluorescent phycocyanin in seawater

Phycocyanin with excellent fluorescence characteristics and important physiological significance is an effective indicator for cyanobacterial bloom assessment due to its close relationship with cyanobacterial biomass. Molecularly imprinted polymers (MIPs) have attracted great interest owing to their recognition specificity; micromotor-driven targeted transport capability holds considerable promise. Herein, we propose an attractive magnetic microsensor for selective recognition, enrichment and transport of label-free fluorescent phycocyanin by combining MIPs and catalytic micromotors. The MIP-based catalytic microsensor was fabricated using phycocyanin as the imprinting molecule, Ni (0.55%) as the magnetic navigation material, and Pt (24.55%) as the solid support/catalyst to facilitate free movement in solutions, as well as an additional magnetic field was employed for trajectory control. The autonomous self-propulsion microsensor vividly displayed their motion states, presenting two different trajectories. The movement velocity was calculated based on the body-deformation model, suggesting a linear positive correlation between the velocity and hydrogen peroxide concentration, with a high average speed of 163 mm s(-1). In addition, highly efficient targeted identification and enrichment abilities were demonstrated based on the magnetically imprinted layer. More excitingly, no obvious interference was found from complicated matrices such as seawater samples, along with real-time visualization of phycocyanin loading and transport. The sensing strategy would not only provide potential applications for rapid microscale monitoring of algae blooms, but also enrich the research connotations of protein imprinting.Phycocyanin with excellent fluorescence characteristics and important physiological significance is an effective indicator for cyanobacterial bloom assessment due to its close relationship with cyanobacterial biomass. Molecularly imprinted polymers (MIPs) have attracted great interest owing to their recognition specificity; micromotor-driven targeted transport capability holds considerable promise. Herein, we propose an attractive magnetic microsensor for selective recognition, enrichment and transport of label-free fluorescent phycocyanin by combining MIPs and catalytic micromotors. The MIP-based catalytic microsensor was fabricated using phycocyanin as the imprinting molecule, Ni (0.55%) as the magnetic navigation material, and Pt (24.55%) as the solid support/catalyst to facilitate free movement in solutions, as well as an additional magnetic field was employed for trajectory control. The autonomous self-propulsion microsensor vividly displayed their motion states, presenting two different trajectories. The movement velocity was calculated based on the body-deformation model, suggesting a linear positive correlation between the velocity and hydrogen peroxide concentration, with a high average speed of 163 mm s(-1). In addition, highly efficient targeted identification and enrichment abilities were demonstrated based on the magnetically imprinted layer. More excitingly, no obvious interference was found from complicated matrices such as seawater samples, along with real-time visualization of phycocyanin loading and transport. The sensing strategy would not only provide potential applications for rapid microscale monitoring of algae blooms, but also enrich the research connotations of protein imprinting

Double water compatible molecularly imprinted polymers applied as solid-phase extraction sorbent for selective preconcentration and determination of triazines in complicated water samples

In the present work, double water compatible molecularly imprinted polymers (DWC-MIPs) with water compatible core and hydrophilic polymer brushes were prepared by reversible addition-fragmentation chain transfer precipitate polymerization (RAFTPP) and applied as solid-phase extraction (SPE) sorbent for selective preconcentration and specific recognition of triazines in water samples. The DWC-MIPs employed as SPE sorbent presented much higher extraction efficiency for four triazines in aqueous media based on the double water compatible property. The validated method was also successfully applied to tap water and river water sample analysis, and satisfactory recoveries were attained, such as 69.2-95.4% with the precision of 1.59-3.94% for four triazines at 100 p.,g L-1. The DWC-MIPs-SPE proves to be a highly effective cleanup and enrichment method for simultaneous separation and sensitive determination of triazines in complicated water samples. (c) 2014 Elsevier B.V. All rights reserved.In the present work, double water compatible molecularly imprinted polymers (DWC-MIPs) with water compatible core and hydrophilic polymer brushes were prepared by reversible addition-fragmentation chain transfer precipitate polymerization (RAFTPP) and applied as solid-phase extraction (SPE) sorbent for selective preconcentration and specific recognition of triazines in water samples. The DWC-MIPs employed as SPE sorbent presented much higher extraction efficiency for four triazines in aqueous media based on the double water compatible property. The validated method was also successfully applied to tap water and river water sample analysis, and satisfactory recoveries were attained, such as 69.2-95.4% with the precision of 1.59-3.94% for four triazines at 100 p.,g L-1. The DWC-MIPs-SPE proves to be a highly effective cleanup and enrichment method for simultaneous separation and sensitive determination of triazines in complicated water samples. (c) 2014 Elsevier B.V. All rights reserved

Naked-eye sensitive ELISA-like assay based on gold-enhanced peroxidase-like immunogold activity

A naked-eye sensitive ELISA-like assay was developed based on gold-enhanced peroxidase-like activity of gold nanoparticles (AuNPs). Using human IgG (H-IgG) as an analytical model, goat anti-human IgG antibody (anti-IgG) adsorbed on microtiter plate and AuNPs-labeled anti-IgG acted as capture antibody and detection antibody, respectively. Because the surfaces of AuNPs were blocked by protein molecules, the peroxidase-like activity of AuNPs was almost inhibited, evaluated by the catalytic oxidation of peroxidase enzyme substrate 3,3',5,5'-tetramethylbenzidine (TMB), which could produce a bright blue color in the presence of H2O2. Fortunately, the catalytic ability of AuNPs was dramatically increased by the deposition of gold due to the formation of a new gold shell on immunogold. Under optimal reaction conditions, the colorimetric immunoassay presented a good linear relationship in the range of 0.7-100 ng/mL and the limit of detection (LOD) of 0.3 ng/mL calculated by 3 sigma/S for UV-vis detection, and obtained LOD of 5 ng/mL for naked-eye detection. The obtained results were competitive with conventional sandwich ELISA with the LOD of 1.6 ng/mL. Furthermore, this developed colorimetric immunoassay was successfully applied to diluted human serum and fetal bovine serum samples, and predicted a broad prospect for the use of peroxidase-like activity involving nanomaterials in bioassay and diagnostics