Modulated growth of nanoparticles. Application for sensing nerve gases

Analyte-mediated formation and growth of nanoparticles for the development of chemical sensors and biosensors

The cornerstone of nanomaterial-based sensing systems is the synthesis of nanoparticles with appropriate surface functionalization that ensures their stability and determines their reactivity with organic or inorganic analytes. To accomplish these requirements, various compounds are used as additives or growth factors to regulate the properties of the synthesized nanoparticles and their reactivity with the target analytes. A different rationale is to use the target analytes as additives or growth agents to control the formation and properties of nanoparticles. The main difference is that the analyte recognition event occurs before or during the formation of nanoparticles and it is based on the reactivity of the analytes with the precursor materials of the nanoparticles (e.g., metal ions, reducing agents, and coatings). The transition from the ionic (or molecular) state of the precursor materials to ordered nanostructured assemblies is used for sensing and signal transduction for the qualitative detection and the quantitative determination of the target analytes, respectively. This review focuses on assays that are based on analyte-mediated regulation of nanoparticles' formation and differentiate them from standard nanoparticle-based assays which rely on pre-synthesized nanoparticles. Firstly, the principles of analyte-mediated nanomaterial sensors are described and then they are discussed with emphasis on the sensing strategies, the signal transduction mechanisms, and their applications. Finally, the main advantages, as well as the limitations of this approach, are discussed and compared with assays that rely on pre-synthesized nanoparticles in order to highlight the major advances accomplished with this type of nano-sensors and elucidate challenges and opportunities for further evolving new nano-sensing strategies.

Recent progress in plasmonic nanoparticle-based biomarker detection and cytometry for the study of central nervous system disorders

Neurological disorders affect hundreds of millions of people around the world, are often life-threatening, untreatable, and can result in debilitating symptoms. The high prevalence of these disorders, which feature biochemical or structural abnormalities in neuronal systems, has spurned innovations in both rapid and early detection to assist in the selection of appropriate treatment strategies to improve the patients' quality of life. Plasmonic nanoparticles (PNPs), a versatile and promising class of nanomaterials, are widely utilized in numerous imaging techniques, drug delivery systems, and biomarker detection methods. Recently, PNP-based nanoprobes have attracted considerable attention for the early diagnosis of neurological disorders. Gold nanoparticles (AuNPs), with high local surface plasmon resonance (LSPR) signals, have been particularly well exploited as probes for dynamic biomarker detection, with quantification sensitivity demonstrated down to the single-molecule level. In this review, we will discuss the possibilities of PNPs in the methodological development for rapid neurological disease identification. In addition, we will also describe a new digital cytometry method that combines dark-field imaging and machine learning for precise biomarker enumeration on single cells. The aim of this review is to attract researchers working on the future development of new plasmonic nanoprobe-based strategies for the diagnosis of neurological disorders.

Dual-mode detection of organophosphate pesticides in pear and Chinese cabbage based on fluorescence and AuNPs colorimetric assays

Herein, a dual-mode method based on fluorescent and colorimetric sensor was developed for determination of organophosphate pesticides (OPs). In this study, indoxyl acetate (IDA) was hydrolyzed by esterase into indophenol. Indophenol leads to changes in fluorescence signal and aggregation of gold nanoparticles (AuNPs); ultimately changing the color from red to blue. When OPs exist, the formation of indophenol was inhibited. With increasing the concentrations of OPs, the enhancement rate of fluorescence signal decreases, and the color change of AuNPs weakened gradually. The assay was applied for determination of dichlorvos, trichlorfon, and paraoxon, and the limits of detection (LODs) were 0.0032 mg/kg, 0.0096 mg/kg, and 0.0074 mg/kg (fluorometric assay), and 0.0120 mg/kg, 0.0224 mg/kg, and 0.0106 mg/kg (colorimetric assay), respectively. Finally, such a convenient and sensitive sensing assay was successfully applied for quantification of OPs in pear and Chinese cabbage with good recoveries ranged between 80.19 and 116.93%.

Colorimetric detection of acetylcholinesterase and its inhibitor based on thiol-regulated oxidase-like activity of 2D palladium square nanoplates on reduced graphene oxide

A convenient and sensitive colorimetric assay for acetylcholinesterase (AChE) and its inhibitor has been designed based on the oxidase-like activity of {100}-faceted Pd square nanoplates which are grown in situ on reduced graphene oxide (PdSP@rGO). PdSP@rGO can effectively catalyze the oxidation of colorless 3,3',5,5'-tetramethylbenzidine (TMB) without the assistance of H₂O₂ to generate blue oxidized TMB (oxTMB) with a characteristic absorption peak at 652 nm. In the presence of AChE, acetylthiocholine (ATCh), a typical AChE substrate, is hydrolyzed to thiocholine (TCh). The generated TCh can effectively inhibit the PdSP@rGO-triggered chromogenic reaction of TMB via cheating with Pd, resulting in color fading and decrease in absorbance. Thus, a sensitive probe for AChE activity is constructed with a working range of 0.25-5 mU mL^-1 and  a limit of detection (LOD) of 0.0625 mU mL^-1. Furthermore, because of the inhibition effect of tacrine on AChE, tacrine is also detected through the colorimetric AChE assay system within the concentrations range 0.025-0.4 μM with a LOD of 0.00229 μM. Hence, a rapid and facile colorimetric procedure to sensitively detect AChE and its inhibitor can be anticipated through modulating the oxidase-like activity of PdSP@rGO. Colorimetric method for detection of AChE and its inhibitor is established by modulating the oxidase mimetic activity of {100}-faceted Pd square nanoplates on reduced graphene oxide (PdSP@rGO).

Development of portable CdS QDs screen-printed carbon electrode platform for electrochemiluminescence measurements and bioanalytical applications

In this work, a portable and disposable screen-printed electrode-based platform for CdS QDs electrochemiluminescence (ECL) detection is presented. CdS QDs were synthesized in aqueous media and placed on top of carbon electrodes by drop casting. The CdS QDs spherical assemblies consisted of nanoparticles about 4 nm diameters and served as ECL sensitizers to enzymatic assays. The nanoparticles were characterized by optical techniques, TEM and XPS. Besides, the electrode modification process was optimized and further studied by SEM and confocal microscopy. The ECL emission from CdS QDs was triggered with H₂O₂ as cofactor and enzymatic assays were employed to modulate the CdS QDs ECL signal by blocking the surface or generating H₂O₂ in situ. Thiol-bearing compounds such as thiocholine generated through the hydrolysis of acetylthiocholine by acetylcholinesterase (AChE) interacted with the surface of CdS QDs thus blocking the ECL. The biosensor showed a linear range up to 5 mU mL^-1 and a detection limit of 0.73 mU mL^-1 for AChE. Moreover, the inhibition mechanism of the enzyme was studied by using 1,5-bis-(4-allyldimethylammonium-phenyl)pentan-3-one dibromide with a detection limit of 79.22 nM. Furthermore, the natural production of H₂O₂ from the oxidation of methanol by the action of alcohol oxidase was utilized to carry out the ECL process. This enzymatic assay presented a linear range up to 0.5 mg L^-1 and a detection limit of 61.46 μg L^-1 for methanol. The reported methodology shows potential applications for the development of sensitive and easy to hand biosensors and was applied to the determination of AChE and methanol in real samples.

Smartphone based highly sensitive visualized detection of acid phosphatase enzyme activity

With the rapid development of point-of-care (POC) technologies, development of sensitive method featured with fast analysis and affordable devices has become an emerging requirement for practical applications. In this study, we introduced a smartphone-based RGB analysis system for the sensitive detection of acid phosphatase (ACP) enzyme activity. In the presence of ACP, l-ascorbic acid 2-phosphate (AAP) can be converted into ascorbic acid (AA), which can reduce Ag⁺ to Ag⁰ and format the Au@Ag core-shell nanostructure. This morphology change of the Au@Ag core-shell would trigger a significant color variation (pink to yellow). A good linear relationship between the RGB model parameter and the concentration of ACP could be obtained with a detection limit of 0.1 U L^-1. Moreover, this sensing strategy is suitable for the detection of ACP in practical serum samples. Thus, this simple but powerful protocol has great potential application for on-site detection of ACP in future complex biological samples.

A review on colorimetric methods for determination of organophosphate pesticides using gold and silver nanoparticles

This review (with 99 refs.) summarizes the progress that has been made in colorimetric (i.e. spectrophotometric) determination of organophosphate pesticides (OPPs) using gold and silver nanoparticles (NPs). Following an introduction into the field, a first large section covers the types and functions of organophosphate pesticides. Methods for colorimetric (spectrophotometric) measurements including RGB techniques are discussed next. A further section covers the characteristic features of gold and silver-based NPs. Syntheses and modifications of metal NPs are covered in section 5. This is followed by overviews on enzyme inhibition-based assays, aptamer-based assays and chemical (non-enzymatic) assays, and a discussion of specific features of colorimetric assays. Several Tables are presented that give an overview on the wealth of methods and materials. A concluding section addresses current challenges and discusses potential future trends and opportunities. Graphical abstractSchematic representation of organophosphate pesticide determinations based on aggregation of nanoparticles (particular silver or gold nanoparticles). This leads to a color change which can be determined visually and monitored by a red shift in the absorption spectrum.

Electrochemical micro analytical device interfaced with portable potentiostat for rapid detection of chlorpyrifos using acetylcholinesterase conjugated metal organic framework using Internet of things

An Electrochemical micro Analytical Device (EµAD) was fabricated for sensitive detection of organophosphate pesticide chlorpyrifos in the food chain. Gold microelectrode (µE) modified with Zinc based Metal Organic Framework (MOF-Basolite Z1200) and Acetylcholinesterase (AChE) enzyme served as an excellent electro-analytical transducer for the detection of chlorpyrifos. Electrochemical techniques such as Cyclic Voltammetry (CV), Electrochemical Impedance Spectroscopy (EIS) and Differential Pulse Voltammetry (DPV) were performed for electrochemical analysis of the developed EµAD. The sensor needs only 2 µL of the analyte and it was tested within the linear range of 10 to 100 ng/L. The developed EµAD’s limit of detection (LoD) and sensitivity is 6 ng/L and 0.598 µ A/ng L⁻¹/mm² respectively. The applicability of the device for the detection of chlorpyrifos from the real vegetable sample was also tested within the range specified. The fabricated sensor showed good stability with a shelf-life of 20 days. The EµAD’s response time is of 50 s, including an incubation time of 20 s. The developed EµAD was also integrated with commercially available low-cost, handheld potentiostat (k-Stat) using Bluetooth and the results were comparable with a standard electrochemical workstation.

Multifunctional Ag@MOF-5@chitosan non-woven cloth composites for sulfur mustard decontamination and hemostasis

Attachment of MOF-5 particles on the surface of carboxymethylated non-woven chitosan cloth (denoted MOF-5@chitosan) was achieved by a layer-by-layer technique in an alternating bath of Zn(OAc)2·2H2O and terephthalic acid solutions. Afterwards, silver nanoparticles were formed/loaded within the resulting MOF-5@chitosan by irradiating at 350 nm wavelength the composite immersed in an aqueous solution of silver nitrate of different concentrations, leading to the formation of ternary composites (denoted Ag@MOF-5@chitosan) which were thoroughly characterized by various techniques. Decontamination of HD over the composites was systematically studied and the results showed that decontamination efficacy increased with the increase of silver amount. The decontamination rate constant and half-life of HD were found to be 0.011 min-1 and 63.0 min over the optimal composite, respectively. Remarkably, attachment of the silver nanoparticles and MOF-5 on the chitosan cloth surface did not interfere with chitosan's original hemostatic capability that was confirmed through the arterial hemostasis of rats. It is expected that the multifunctional composite material can find practical applications in the fields of hemostasis, sterilization and chemical war agent decontamination.

Generic Assay of Sulfur-Containing Compounds Based on Kinetics Inhibition of Gold Nanoparticle Photochemical Growth

This work describes a new, equipment-free, generic method for the determination of sulfur-containing compounds that is based on their ability to slow down the photoreduction kinetics of gold ions to gold nanoparticles. The method involves tracking the time required for a red coloration to appear in the tested sample, indicative of the formation of gold nanoparticles, and compare the measured time relative to a control sample in the absence of the target analyte. The method is applicable with minimal and simple steps requiring only two solutions (i.e., a buffer and a gold solution), a source of light (UV or visible), and a timer. The method responds to a large variety of sulfur-containing compounds including thiols, thioesters, disulfides, thiophosphates, metal-sulfur bonds, and inorganic sulfur and was therefore applied to the determination of a variety of compounds such as dithiocarbamate and organophosphorous pesticides, biothiols, pharmaceutically active compounds, and sulfides in different samples such as natural waters and wastewater, biological fluids, and prescription drugs. The analytical figures of merit of the method include satisfactory sensitivity (quantitation limits at the low μM levels), good recoveries (from 93 to 109%), and satisfactory reproducibility (from 4.8 to 9.8%). The method is easily adoptable to both laboratory settings and nonlaboratory conditions for quantitative and semiquantitative analysis, respectively, is user-friendly even for the minimally trained user, and can be performed with limited resources at low cost.

Kinetic investigation for the catalytic reduction of nitrophenol using ionic liquid stabilized gold nanoparticles

We demonstrate the synthesis of gold nanoparticles (AuNP) stabilized by 1-butyl-3-hexadecyl imidazolium bromide (Au@[C₄C₁₆Im]Br) and their use as a catalyst for the reduction of nitrophenol. The AuNPs show excellent stability in presence of [C₄C₁₆Im]Br ionic liquids for the reduction of 4-nitrophenol and 2-nitrophenol using NaBH₄ as a reducing agent. The detailed kinetics for the reduction of 4-nitrophenol and 2-nitrophenol were investigated and the catalytic activity of Au@[C₄C₁₆Im]Br was evaluated. The pseudo first-order rate constant (k_app) values for 4-nitrophenol was observed to be greater than that of 2-nitrophenol and explained on the basis of hydrogen bonding present in 2-nitrophenol. Au@[C₄C₁₆Im]Br showed good separability and reusability and hence, it can be used for the complete reduction of nitrophenols in multiple cycles. The Langmuir–Hinshelwood reaction mechanism is elucidated for reduction of 4-nitrophenol by Au@[C₄C₁₆Im]Br nanocatalyst on the basis of the k_app values. The thermodynamic activation parameters such as activation energy, enthalpy of activation and entropy of activation were determined and explained using the temperature dependent kinetics for the reduction of nitrophenol using Au@[C₄C₁₆Im]Br. The above results reveal that the Au@[C₄C₁₆Im]Br nanocatalyst demonstrates excellent catalytic performance for the reduction of nitrophenol by NaBH₄ at room temperature.

Catalytic reduction of nitrophenol using ionic liquid stabilized AuNPs.

Biosensing strategies based on enzymatic reactions and nanoparticles

Application of new nanomaterials to detection of enzymatic activities allows the development of new sensitive and selective bioanalytical assays based on enzymes for recognition and signal amplification.

A novel enzyme-mediated gold nanoparticle synthesis and its application forin situdetection of horseradish peroxidase inhibitor phenylhydrazine

Biocatalyzed gold nanoparticle synthesis for thein situdetection of horseradish peroxidase inhibitor (phenylhydrazine) has been demonstrated.

Blocked Enzymatic Etching of Gold Nanorods: Application to Colorimetric Detection of Acetylcholinesterase Activity and Its Inhibitors

The anisotropic morphology of gold nanorods (AuNRs) has been shown to lead to nonuniform ligand distribution and preferential etching through their tips. We have recently demonstrated that this effect can be achieved by biocatalytic oxidation with hydrogen peroxide, catalyzed by the enzyme horseradish peroxidase (HRP). We report here that modification of AuNRs with thiol-containing organic molecules such as glutathione and thiocholine hinders enzymatic AuNR etching. Higher concentrations of thiol-containing molecules in the reaction mixture gradually decrease the rate of enzymatic etching, which can be monitored by UV-vis spectroscopy through changes in the AuNR longitudinal plasmon band. This effect can be applied to develop novel optical assays for acetylcholinesterase (AChE) activity. The biocatalytic hydrolysis of acetylthiocholine by AChE yields thiocholine, which prevents enzymatic AuNR etching in the presence of HRP. Additionally, the same bioassay can be used for the detection of nanomolar concentrations of AChE inhibitors such as paraoxon and galanthamine.

Acetylcholinesterase (AChE)-mediated immobilization of silver nanoparticles for the detection of organophosphorus pesticides

We report an enzyme-mediated biosensor with the immobilization of silver nanoparticles (AgNPs) for the detection of organophosphorus (OP) pesticides.

Visualizing dopamine released from living cells using a nanoplasmonic probe

We report the development of an ultrasensitive nanoplasmonic probe for discriminative detection and imaging of dopamine released from living cells. The sensing mechanism is based on the dopamine-induced seeded-growth of Au nanoparticles (Au NPs) that leads to the shift of the plasmon band. This platform allows for the detection of dopamine with a detection limit down to 0.25 pM within 1 min. This nanoplasmonic assay is further applied to visualize the release of dopamine from living rat pheochromocytoma (PC12) cells under ATP-stimulation with dark-field microscopy (DFM). The DFM results together with real time fluorescence imaging of PC12 cells stained with the Fluo calcium indicator, suggested that ATP stimulated-release of dopamine is concomitant with the Ca(2+) influx, and the influx of Ca(2+) is through ATP-activated channels instead of the voltage-gated Ca(2+) channel (VGC).

Enzymatic reaction modulated gold nanorod end-to-end self-assembly for ultrahigh sensitively colorimetric sensing of cholinesterase and organophosphate pesticides in human blood

We present herein the first reported self-assembly modulation of gold nanorods (AuNRs) by enzymatic reaction, which is further employed for colorimetric assays of cholinesterase (ChE) and organophosphate pesticides (OPs) in human blood. ChE catalyzes its substrate (acetylthiocholine) and produces thiocholine and acetate acid. The resulting thiols then react with the tips of the AuNRs by S-Au conjunction and prevent subsequent cysteine-induced AuNR end-to-end (EE) self-assembly. Correspondingly, the AuNR surface plasmon resonance is regulated, which results in a distinctly ratiometric signal output. Under optimal conditions, the linear range is 0.042 to 8.4 μU/mL, and the detection limit is as low as 0.018 μU/mL. As ChE is incubated with OPs, the enzymatic activity is inhibited. So, the cysteine-induced assembly is observed again. On the basis of this principle, OPs can be well determined ranging from 0.12 to 40 pM with a 0.039 pM detection limit. To our knowledge, the present quasi pU/mL level sensitivity for ChE and the quasi femtomolar level sensitivity for OPs are at least 500 and 7000 times lower than those of previous colorimetric methods, respectively. The ultrahigh sensitivity results from (1) the rational choice of anisotropic AuNRs as building blocks and reporters and (2) the specific structure of the enzymatic thiocholine. Because of ultrahigh sensitivity, serum samples are allowed to be extremely diluted in the assay. Accordingly, various nonspecific interactions, even from glutathione/cysteine, are well avoided. So, both ChE and OPs in human blood can be directly assayed without any prepurification, indicating the simplicity and practical promise of the proposed method.

A plasmonic nanosensor for lipase activity based on enzyme-controlled gold nanoparticles growth in situ

A plasmonic nanosensor for lipase activity was developed based on one-pot nanoparticle growth. Tween 80 was selected not only as the substrate for lipase recognition but also as the reducing and stabilizing agent for the sensor fabrication. The different molecular groups in Tween 80 could have different roles in the fabrication procedure; the H2O2 produced by the autoxidation of the ethylene oxide subunits in Tween 80 could reduce the AuCl4(-) ions to Au atoms, meanwhile, the lipase could hydrolyze its carboxyl ester bond, which could, in turn, control the rate of nucleation of the gold nanoparticles (AuNPs) and tailor the localized surface plasmon resonance (LSPR) of the AuNP transducers. The color changes, which depend on the absence or presence of the lipase, could be used to sense the lipase activity. A linear response ranging from 0.025 to 4 mg mL(-1) and a detection limit of the lipase as low as 3.47 μg mL(-1) were achieved. This strategy circumvents the problems encountered by general enzyme assays that require sophisticated instruments and complicated assembling steps. The methodology can benefit the assays of heterogeneous-catalyzed enzymes.

Developing acetylcholinesterase-based inhibition assay by modulated synthesis of silver nanoparticles: applications for sensing of organophosphorus pesticides

A novel and highly sensitive probe for the detection of organophosphorus compounds (OPs) using acetylcholinesterase (AChE) and acetylthiocholine (ATCh) during the modulated synthesis of silver nanoparticles.

Nanomaterials-based optical techniques for the detection of acetylcholinesterase and pesticides

The large amount of pesticide residues in the environment is a threat to global health by inhibition of acetylcholinesterase (AChE). Biosensors for inhibition of AChE have been thus developed for the detection of pesticides. In line with the rapid development of nanotechnology, nanomaterials have attracted great attention and have been intensively studied in biological analysis due to their unique chemical, physical and size properties. The aim of this review is to provide insight into nanomaterial-based optical techniques for the determination of AChE and pesticides, including colorimetric and fluorescent assays and surface plasmon resonance.

Cysteine-mediated aggregation of Au nanoparticles: the development of a H2O2 sensor and oxidase-based biosensors

The cysteine-stimulated aggregation of Au nanoparticles (Au NPs) is used as an auxiliary reporting system for the optical detection of H2O2, for optical probing of the glucose oxidase (GOx) and the catalyzed oxidation of glucose, for probing the biocatalytic cascade composed of acetylcholine esterase/choline oxidase (AChE/ChOx), and for following the inhibition of AChE. The analytical paradigm is based on the I(-)-catalyzed oxidation of cysteine by H2O2 to cystine, a process that prohibits the cysteine-triggered aggregation of the Au NPs. The system enabled the analysis of H2O2 with a detection limit of 2 μM. As the GOx-biocatalyzed oxidation of glucose yields H2O2, and the AChE/ChOx cascade leads to the formation of H2O2, the two biocatalytic processes could be probed by the cysteine-stimulated aggregation of the Au NPs. Since AChE is inhibited by 1,5-bis(4-allyldimethylammonium phenyl)pentane-3-one dibromide, the biocatalytic AChE/ChOx cascade is inhibited by the inhibitor, thus leading to the enhanced cysteine-mediated aggregation of the NPs. The results suggest the potential implementation of the cysteine-mediated aggregation of Au NPs in the presence of AChE/ChOx as a sensing platform for the optical detection of chemical warfare agents.

Multifunctional gold nanoparticles for diagnosis and therapy of disease

Gold nanoparticles (AuNPs) have a number of physical properties that make them appealing for medical applications. For example, the attenuation of X-rays by gold nanoparticles has led to their use in computed tomography imaging and as adjuvants for radiotherapy. AuNPs have numerous other applications in imaging, therapy and diagnostic systems. The advanced state of synthetic chemistry of gold nanoparticles offers precise control over physicochemical and optical properties. Furthermore gold cores are inert and are considered to be biocompatible and nontoxic. The surface of gold nanoparticles can easily be modified for a specific application, and ligands for targeting, drugs or biocompatible coatings can be introduced. AuNPs can be incorporated into larger structures such as polymeric nanoparticles or liposomes that deliver large payloads for enhanced diagnostic applications, efficiently encapsulate drugs for concurrent therapy or add additional imaging labels. This array of features has led to the aforementioned applications in biomedical fields, but more recently in approaches where multifunctional gold nanoparticles are used for multiple methods, such as concurrent diagnosis and therapy, so-called theranostics. This review covers basic principles and recent findings in gold nanoparticle applications for imaging, therapy and diagnostics, with a focus on reports of multifunctional AuNPs.

Critical evaluation of acetylthiocholine iodide and acetylthiocholine chloride as substrates for amperometric biosensors based on acetylcholinesterase

Numerous amperometric biosensors have been developed for the fast analysis of neurotoxic insecticides based on inhibition of cholinesterase (AChE). The analytical signal is quantified by the oxidation of the thiocholine that is produced enzymatically by the hydrolysis of the acetylthiocholine pseudosubstrate. The pseudosubstrate is a cation and it is associated with chloride or iodide as corresponding anion to form a salt. The iodide salt is cheaper, but it is electrochemically active and consequently more difficult to use in electrochemical analytical devices. We investigate the possibility of using acetylthiocholine iodide as pseudosubstrate for amperometric detection. Our investigation demonstrates that operational conditions for any amperometric biosensor that use acetylthiocholine iodide must be thoroughly optimized to avoid false analytical signals or a reduced sensitivity. The working overpotential determined for different screen-printed electrodes was: carbon-nanotubes (360 mV), platinum (560 mV), gold (370 mV, based on a catalytic effect of iodide) or cobalt phthalocyanine (110 mV, but with a significant reduced sensitivity in the presence of iodide anions).

Gold nanoparticle-based optical microfluidic sensors for analysis of environmental pollutants

Conventional methods of environmental analysis can be significantly improved by the development of portable microscale technologies for direct in-field sensing at remote locations. This report demonstrates the vast potential of gold nanoparticle-based microfluidic sensors for the rapid, in-field, detection of two important classes of environmental contaminants - heavy metals and pesticides. Using gold nanoparticle-based microfluidic sensors linked to a simple digital camera as the detector, detection limits as low as 0.6 μg L(-1) and 16 μg L(-1) could be obtained for the heavy metal mercury and the dithiocarbamate pesticide ziram, respectively. These results demonstrate that the attractive optical properties of gold nanoparticle probes combine synergistically with the inherent qualities of microfluidic platforms to offer simple, portable and sensitive sensors for environmental contaminants.

Enzymatic growth of quantum dots: applications to probe glucose oxidase and horseradish peroxidase and sense glucose

Three innovative assays are developed for the detection of enzymatic activities of glucose oxidase (GOx) and horseradish peroxidase (HRP) by the generation of CdS quantum dots (QDs) in situ using non-conventional enzymatic reactions. In the first assay, GOx catalyzes the oxidation of 1-thio-β-D-glucose to give 1-thio-β-D-gluconic acid. The latter is spontaneously hydrolyzed to β-D-gluconic acid and H2 S, which in the presence of cadmium nitrate yields fluorescent CdS nanoparticles. In the second assay HRP catalyzes the oxidation of sodium thiosulfate with hydrogen peroxide generating H2 S and consequently CdS QDs. The combination of GOx with HRP, allowed quantification of glucose in plasma by following growth of fluorescent QDs.

Highly sensitive colorimetric detection of organophosphate pesticides using copper catalyzed click chemistry

Highly sensitive colorimetric detection of organophosphate pesticides (OPs) was developed using Cu (I)-catalyzed click chemistry as the colorimetric signal amplification process between the acetylcholine esterase-acetylthiocholine system (AChE-ATCl) and azide- terminal alkyne-functionalized Au NPs as the colorimetric probe. It was demonstrated that the involvement of Cu (I)-catalyzed click chemistry allowed greatly improved colorimetric sensitivity for OPs detection based on the indirect modulation of click chemistry-induced Au NPs aggregation by the AChE-ATCl system. Paraoxon as the model OPs in the concentration range from 10(-6) to 10(-4)g/L can be directly detected using the naked-eye-based colorimetric assay without the aid of any complex instruments. The results for paraoxon detection in spiked apple juice were found to be in good agreement with that obtained by the conventional UV-vis spectroscopy. This simple and reliable assay would greatly improve the public safety and environmental protection in an on-site and real-time detection format.

Quantification of prothrombin in human plasma amplified by autocatalytic reaction

By site directed mutagenesis, we have produced recombinant mutants of human and mouse prethrombin-2 which are able to convert themselves autocatalytically into α-thrombin. We also have created a new method to amplify the signal of bioanalytical assays based on the autocatalytic activation of these mutated proenzymes. The activation of the mutants by active α-thrombin triggers an autocatalytic reaction which leads to more active thrombin resulting in the amplification of the readout signal. Addition of mutated mouse prethrombin-2 into the conventional assay for prothrombin level in human plasma, employing ecarin and the fluorogenic substrate, resulted in improvement of the detection limit by 2 orders of magnitude.