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

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

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

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

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

A near-infrared ratiometric fluorescent probe for cysteine detection over glutathione indicating mitochondrial oxidative stress in vivo

We establish a near-infrared (NIR) ratiometric fluorescent probe Cy-NB for the selective detection of cysteine (Cys) over glutathione (GSH) and homocysteine (Hcy) in mitochondria to indicate oxidative stress. Heptamethine cyanine dye is chosen as the fluorophore of Cy-NB whose emission locates in NIR region. And p-nitrobenzoyl is employed as the fluorescent modulator due to its capability of selective-Cys response. Once triggered by Cys, the uncaged p-nitrobenzoyl rearranges the polymethine pi-electron system of the fluorophore, which leads to a remarkable spectrum shifts in absorption and emission profiles. Taking advantage of these spectroscopic properties, we construct a ratiometric fluorescent signal for the detection of Cys with a detection limit of 0.2 mu M within 5 min. Our probe Cy-NB can sensitively detect the mitochondrial Cys pool changes under different oxidative stress status in HepG2 cells. We also successfully employ Cy-NB to imaging Cys level changes in living mice. It suggests that mitochondrial Cys can be used as an oxidative stress biomarker with simple potential clinical applications. And our probe Cy-NB is of great potential for further utilizing in exploring the physiological function of Cys in biological systems. (C) 2015 Elsevier B.V. All rights reserved.We establish a near-infrared (NIR) ratiometric fluorescent probe Cy-NB for the selective detection of cysteine (Cys) over glutathione (GSH) and homocysteine (Hcy) in mitochondria to indicate oxidative stress. Heptamethine cyanine dye is chosen as the fluorophore of Cy-NB whose emission locates in NIR region. And p-nitrobenzoyl is employed as the fluorescent modulator due to its capability of selective-Cys response. Once triggered by Cys, the uncaged p-nitrobenzoyl rearranges the polymethine pi-electron system of the fluorophore, which leads to a remarkable spectrum shifts in absorption and emission profiles. Taking advantage of these spectroscopic properties, we construct a ratiometric fluorescent signal for the detection of Cys with a detection limit of 0.2 mu M within 5 min. Our probe Cy-NB can sensitively detect the mitochondrial Cys pool changes under different oxidative stress status in HepG2 cells. We also successfully employ Cy-NB to imaging Cys level changes in living mice. It suggests that mitochondrial Cys can be used as an oxidative stress biomarker with simple potential clinical applications. And our probe Cy-NB is of great potential for further utilizing in exploring the physiological function of Cys in biological systems. (C) 2015 Elsevier B.V. All rights reserved

m-Cresol purple functionalized surface enhanced Raman scattering paper chips for highly sensitive detection of pH in the neutral pH range

 Herein, a pH sensitive paper SERS chip was prepared by selecting m-cresol purple, a molecule with halochromic properties in the neutral pH range as a Raman reporter. The adsorbed m-cresol purple underwent a reversible change in its electronic configuration from a non-resonant species to a resonant species, which resulted in a significant Raman signal intensity variation due to the transformation of the sensing mode from SERS to surface-enhanced resonance Raman scattering (SERRS). The chips have a sensitive pH range of 6.0 to 8.0 and exhibited good performance for the detection of natural water samples with detection precision of approximately 0.03 pH units, suggesting great potential for environmental pH monitoring applications

Mesoporous titania based yolk-shell nanoparticles as multifunctional theranostic platforms for SERS imaging and chemo-photothermal treatment

Recently surface-enhanced Raman scattering (SERS) imaging guided theranostic nanoplatforms have attracted considerable attention. Herein, we developed novel yolk-shell gold nanorod@void@mesoporous titania nanoparticles (AuNR@void@mTiO(2) NPs) for simultaneous SERS imaging and chemo-photothermal therapy. Our work showed three highlighted features: first, we proposed a facile and versatile "up to down" SERS labeling strategy for the drug delivery system, in which "empty carriers" were pre-synthesized, followed by co-loading of Raman reporters on AuNR and anti-cancer drug doxorubicin (DOX) in mTiO(2) in sequence. The acquired SERS signal was strong enough for tracking NPs at both living cells and mice levels. Second, we selected mTiO(2) as a novel drug loading material instead of the widely used mesoporous silica (mSiO(2)). The mTiO(2) shared satisfactory drug loading and release behavior as mSiO(2) but it was chemically inert. This property not only provided a facile way to form a yolk-shell structure but also rendered it with superior structural stability in a biological system. Third, the near infrared (NIR) light absorbing property of the AuNR SERS substrate was also explored for drug release regulation and photothermal treatment. Significantly greater MCF-7 cell killing was observed when treated together with DOX-loaded NPs and NIR laser irradiation, attributable to the synergistic chemo-thermal therapeutic effect. Our results indicated the established SERS labeled yolk-shell NP as a promising theranostic platform and suggested its potential in vivo applications.Recently surface-enhanced Raman scattering (SERS) imaging guided theranostic nanoplatforms have attracted considerable attention. Herein, we developed novel yolk-shell gold nanorod@void@mesoporous titania nanoparticles (AuNR@void@mTiO(2) NPs) for simultaneous SERS imaging and chemo-photothermal therapy. Our work showed three highlighted features: first, we proposed a facile and versatile "up to down" SERS labeling strategy for the drug delivery system, in which "empty carriers" were pre-synthesized, followed by co-loading of Raman reporters on AuNR and anti-cancer drug doxorubicin (DOX) in mTiO(2) in sequence. The acquired SERS signal was strong enough for tracking NPs at both living cells and mice levels. Second, we selected mTiO(2) as a novel drug loading material instead of the widely used mesoporous silica (mSiO(2)). The mTiO(2) shared satisfactory drug loading and release behavior as mSiO(2) but it was chemically inert. This property not only provided a facile way to form a yolk-shell structure but also rendered it with superior structural stability in a biological system. Third, the near infrared (NIR) light absorbing property of the AuNR SERS substrate was also explored for drug release regulation and photothermal treatment. Significantly greater MCF-7 cell killing was observed when treated together with DOX-loaded NPs and NIR laser irradiation, attributable to the synergistic chemo-thermal therapeutic effect. Our results indicated the established SERS labeled yolk-shell NP as a promising theranostic platform and suggested its potential in vivo applications

Uniform core-shell molecularly imprinted polymers: a correlation study between shell thickness and binding capacity

Core-shell molecularly imprinted polymers (CS-MIPs) have aroused increasing interest owing to their easy accessibility and favorable mass transfer. Herein, we explore the correlation between shell thickness and binding capacity by using Sudan I as template molecule to prepare different CS-MIPs at the surface of carboxyl polystyrene through emulsion polymerization with a two-step temperature-rising process. Extensive characterization was performed using techniques such as SEM/TEM, FT-IR, BET, and TGA. Main factors were systematically studied such as the amount of prepolymer solution, the amount of SDS, and the temperature step. Under the optimized conditions, CS-MIPs with a shell thickness of 2.60 mu m presented the highest binding capacity of 30.1 mu mol g(-1) and the most rapid mass transfer rate. A uniform sphere model was constructed, and it was found that template molecules located in the spherical MIPs with a diameter of 5.20 mu m will be completely eluted, thereby attaining the maximum binding capacity. The static adsorption isotherm followed the Langmuir-Freundlich adsorption model, and the fast kinetics obeyed the pseudo-second-order kinetics model. High recognition specificity for Sudan I with respect to its analogues was displayed, with an imprinting factor of 2.7. The establishment of a critical value of shell thickness provides new insights into the preparation methodology and molecular recognition mechanism of core-shell imprinted polymers.Core-shell molecularly imprinted polymers (CS-MIPs) have aroused increasing interest owing to their easy accessibility and favorable mass transfer. Herein, we explore the correlation between shell thickness and binding capacity by using Sudan I as template molecule to prepare different CS-MIPs at the surface of carboxyl polystyrene through emulsion polymerization with a two-step temperature-rising process. Extensive characterization was performed using techniques such as SEM/TEM, FT-IR, BET, and TGA. Main factors were systematically studied such as the amount of prepolymer solution, the amount of SDS, and the temperature step. Under the optimized conditions, CS-MIPs with a shell thickness of 2.60 mu m presented the highest binding capacity of 30.1 mu mol g(-1) and the most rapid mass transfer rate. A uniform sphere model was constructed, and it was found that template molecules located in the spherical MIPs with a diameter of 5.20 mu m will be completely eluted, thereby attaining the maximum binding capacity. The static adsorption isotherm followed the Langmuir-Freundlich adsorption model, and the fast kinetics obeyed the pseudo-second-order kinetics model. High recognition specificity for Sudan I with respect to its analogues was displayed, with an imprinting factor of 2.7. The establishment of a critical value of shell thickness provides new insights into the preparation methodology and molecular recognition mechanism of core-shell imprinted polymers

Stimuli-responsive molecularly imprinted polymers: versatile functional materials

Stimuli-responsive molecularly imprinted polymers (SR-MIPs) have received widespread attention with the rapid development of stimuli responsive polymers and molecularly imprinted polymers, and significant progress has been achieved in recent years in the field of SR-MIPs. To date, magnetic responsive MIPs, temperature responsive MIPs, pH responsive MIPs, photo-responsive MIPs, and dual or multi stimuli responsive MIPs have been prepared, and display broad application perspectives in many fields such as drug delivery, biotechnology, separation sciences, and chemo/biosensors. In the present feature article, those SR-MIPs are summarized comprehensively, and particular attention is paid to the mechanism of SR-MIPs, their preparation methods, and the application aspects. Finally, some significant attempts to further develop SR-MIPs are also proposed.Stimuli-responsive molecularly imprinted polymers (SR-MIPs) have received widespread attention with the rapid development of stimuli responsive polymers and molecularly imprinted polymers, and significant progress has been achieved in recent years in the field of SR-MIPs. To date, magnetic responsive MIPs, temperature responsive MIPs, pH responsive MIPs, photo-responsive MIPs, and dual or multi stimuli responsive MIPs have been prepared, and display broad application perspectives in many fields such as drug delivery, biotechnology, separation sciences, and chemo/biosensors. In the present feature article, those SR-MIPs are summarized comprehensively, and particular attention is paid to the mechanism of SR-MIPs, their preparation methods, and the application aspects. Finally, some significant attempts to further develop SR-MIPs are also proposed