Rapid and visual identification of β-lactamase subtypes for precision antibiotic therapy

The abuse of antibiotics urgently requires rapid identification of drug-resistant bacteria at the point of care (POC). Here we report a visual paper sensor that allows rapid (0.25-3 h) discrimination of the subtypes of β-lactamase (the major cause of bacterial resistance) for precision antibiotic therapy. The sensor exhibits high performance in identifying antibiotic-resistant bacteria with 100 real samples from patients with diverse bacterial infections, demonstrating 100% clinical sensitivity and specificity. Further, this sensor can enhance the accuracy of antibiotic use from 48% empirically to 83%, and further from 50.6% to 97.6% after eliminating fungal infection cases. Our work provides a POC testing platform for guiding effective management of bacterial infections in both hospital and community settings.

Gold Nanoparticle-Based Colorimetric Biosensing for Foodborne Pathogen Detection

Ensuring safe high-quality food is an ongoing priority, yet consumers face heightened risk from foodborne pathogens due to extended supply chains and climate change in the food industry. Nanomaterial-based assays are popular and have recently been developed to ensure food safety and high quality. This review discusses strategies for utilizing gold nanoparticles in colorimetric biosensors. The visible-signal biosensor proves to be a potent sensing technique for directly measuring targets related to foodborne pathogens in the field of food analysis. Among visible-signal biosensors, the localized surface plasmon resonance (LSPR) biosensor has garnered increasing attention and experienced rapid development in recent years. This review succinctly introduces the origin of LSPR theory, providing detailed insights into its fundamental principles. Additionally, this review delves into the application of nanotechnology for the implementation of the LSPR biosensor, exploring methods for utilizing gold nanoparticles and elucidating the factors that influence the generation of visible signals. Several emerging technologies aimed at simple and rapid immunoassays for onsite applications have been introduced in the food industry. In the foreseeable future, field-friendly colorimetric biosensors could be adopted in food monitoring systems. The onsite and real-time detection of possible contaminants and biological substances in food and water is essential to ensure human health and safety.

A biosensor for S100B detection based on PSS-MA-GoldMag-LFIA in early clinical diagnosis of brain damage

S100B is an essential biomarker in the early diagnosis and treatment monitoring of brain injury. However, the traditional clinical diagnostic assay for S100B detection requires a complex operation or large equipment, which limits its application for rapid point-of-care tests (POCT). This study aimed to establish a lateral-flow immunoassay (LFIA) strip test system for S100B determination. PSS-MA-GoldMag nanoparticles were conjugated with anti-S100B antibodies as probes. Using this antibody-nanoparticle composite, an LFIA system based on magnetic quantification was established for S100B detection. For the evaluation of the performance of this LFIA system in clinical practice, 216 clinical samples were assayed using the LFIA test system and a commercial ECLI kit. Using the LFIA system, reliable results could be obtained in 30 min with a detection limit of 0.05 ng mL-1. The coefficient of variation (CV) was <13.8% and <14.03% for intra- and inter-assay precision, respectively. The recoveries were between 95.1 and 107.3%. The relative deviation of the interference experiments was <10%. In the analysis of clinical samples, the result indicated that the sera level of S100B in the detection group did not correlate with gender (p = 0.564 > 0.05) or age (p = 0.083 > 0.05). There is a good correlation between the novel method and the Elecsys®, with a determination coefficient of R2 0.9566, p > 0.05. The Bland-Altman analysis between the two ways shows that the 95% confidence bands between the two methods in measuring S100B were -0.27 ng mL-1 to +0.29 ng mL-1 with a mean difference of +0.006 ng mL-1. These results indicated that the novel LFIA system could be a simple, rapid, convenient, and accurate method for S100B determination.

β-Lactamase Sensitive Probe for Rapid Detection of Antibiotic-Resistant Bacteria with Gas Chromatography–Tandem Mass Spectrometry

β-Lactamase (Bla) produced by bacteria to resist β-lactam antibiotics is a serious public health threat. Developing efficient diagnostic protocols for drug-resistant bacteria is of great significance. In this work, based on gas molecules in bacteria, a novel research strategy was proposed to develop a gas molecule-based probe by grafting 2-methyl-3-mercaptofuran (MF) onto cephalosporin intermediates via a nucleophilic substitution reaction. The probe can release the corresponding MF by reacting with Bla. The released MF, as a marker of drug-resistant bacteria, was analyzed by headspace solid-phase microextraction coupled with gas chromatography-mass spectrometry. The Bla concentration as low as 0.2 nM can be easily observed, providing an efficient method for detecting enzyme activity and screening drug-resistant strains in vivo. Importantly, the method is universal, and probes with different properties can be prepared by changing different substrates to further identify different types of bacteria, thereby broadening the research methods and ideas for monitoring physiological processes.

Near Infrared-II Photothermal and Colorimetric Synergistic Sensing for Intelligent Onsite Dietary Myrosinase Profiling

Myrosinase (Myr) is a type of critical β-thioglucosidase enzyme activator essential for sustaining many functional foods to perform their health-promoting functions. An accurate and reliable Myr test is meaningful for food quality and dietary nutrition assessments, whereas the currently reported methods do not guarantee specificity and have high reliance on instrumentation, which are not suitable for rapid and onsite Myr screening especially in complex systems from various sources. Herein, we present a unique NIR-II absorption-based photothermal-responsive colorimetric biosensor for anti-interference onsite Myr determination and realization of rapid visualized outputs with the aid of smartphone calculation. Typically, assisted by glucose oxidase (GOx), Myr specifically converts the sinigrin substrate into hydrogen peroxide (H₂O₂) that can oxidize 3,3',5,5'-tetramethylbenzidine (TMB) catalyzed by AuNPs to form a charge transfer complex (CTC) with NIR-II absorption and photothermal characters. Delightfully, such a proposed method is able to determine Myr within a wide range of 0 to 172.5 mU/mL with a detection limit down to 2.96 mU/mL. Moreover, simple, rapid, and real-time visual Myr identification in actual food-sourced samples could also be readily achieved by smartphone readout processing, with the promising advantages of anti-interference, high accuracy, and low cost as well as labor-saving and intelligence engagement, thus providing great feasibility for precise measurement in complex and dynamic dietary sample analysis. Overall, our proposed method presents a novel technology for onsite dietary Myr enzyme profiling, which is promising to be applied in the food industry for nutritional composition profiles, freshness evaluation, and quality assessment.

β-Lactamase-Responsive Probe for Efficient Photodynamic Therapy of Drug-Resistant Bacterial Infection

Several photosensitizers have recently been proposed as novel approaches against β-lactamase-producing drug-resistant bacteria. However, these reported photosensitizers are rarely used for accurate recognition of drug-resistant bacteria. To tackle this challenge, the structurally modified photosensitizer CySG-2 based on a lipophilic cationic heptamethine indocyanine near-infrared (NIR) dye (IR-780) and an important synthesis intermediate of cephalosporin antibiotic (GCLE) not only achieved the accurate recognition of TEM-1 methicillin-resistant Staphylococcus aureus (MRSA) successfully but also achieved antimicrobial photodynamic therapy (aPDT) in animal models infected by drug-resistant bacteria. Accurate enzyme recognition and efficient photodynamic therapy capabilities allow CySG-2 to achieve one stone with two birds. In addition, CySG-2 could also promote the eradication of internalized MRSA by facilitating the autophagy process, which is synergistic with its capacity of inducing reactive oxygen species generation under NIR laser irradiation for aPDT. Collectively, it is an effective multifunctional photosensitizer with the potential ability to guide the optimal use of different antibiotics and apply them in clinical treatment.

LSPR-based colorimetric biosensing for food quality and safety

Ensuring consistently high quality and safety is paramount to food producers and consumers alike. Wet chemistry and microbiological methods provide accurate results, but those methods are not conducive to rapid, onsite testing needs. Hence, many efforts have focused on rapid testing for food quality and safety, including the development of various biosensors. Herein, we focus on a group of biosensors, which provide visually recognizable colorimetric signals within minutes and can be used onsite. Although there are different ways to achieve visual color-change signals, we restrict our focus on sensors that exploit the localized surface plasmon resonance (LSPR) phenomenon of metal nanoparticles, primarily gold and silver nanoparticles. The typical approach in the design of LSPR biosensors is to conjugate biorecognition ligands on the surface of metal nanoparticles and allow the ligands to specifically recognize and bind the target analyte. This ligand-target binding reaction leads to a change in color of the test sample and a concomitant shift in the ultraviolet-visual absorption peak. Various designs applying this and other signal generation schemes are reviewed with an emphasis on those applied for evaluating factors that compromise the quality and safety of food and agricultural products. The LSPR-based colorimetric biosensing platform is a promising technology for enhancing food quality and safety. Aided by the advances in nanotechnology, this sensing technique lends itself easily for further development on field-deployable platforms such as smartphones for onsite and end-user applications.

Fluorescent Mesoporous Nanoparticles for β-Lactamase Screening Assays

We present a sensitive and rapid screening method for the determination of β-lactamase activity of antibiotic-resistant bacteria, by designing a pH-sensitive fluorescent dye-doped mesoporous silica nanoparticle encapsulated with penicillin G as a substrate. When penicillin G was hydrolysed by β-lactamase and converted into penicilloic acid, the acidic environment resulted in fluorescence quenching of the dye. The dye-doped mesoporous nanoparticles not only enhanced the β-lactamase-catalyzed reaction rate but also stablized the substrate, penicillin G, which degrades into penicilloic acid in a water solution without β-lactamase. Twentyfive clinical bacterial samples were tested and the antibiotic resistant and susceptible strains were identified. The proposed method may detect the presence of β -lactamases of clinically relevant samples in less than 1 hour. Moreover, the detection limit of β-lactamase activity was as low as 7.8×10-4 U/mL, which was determined within two hours.

Metallic Nanoparticle-Enabled Sensing of a Drug-of-Abuse: An Attempt at Forensic Application

γ-Hydroxybutyric acid (GHB) functions as a depressant on the central nerve system and serves as a pharmaceutical agent in the treatment of narcolepsy and alcohol withdraw. In recent years, GHB has been misused as a recreational drug due to its ability to induce euphoric feelings. Moreover, it has gained increasing attention as a popular drug of abuse that is frequently related to drug-facilitated sexual assaults. At the moment, detection methods based on chromatography exhibit extraordinary sensitivity for GHB sensing. However, such techniques require complicated sample treatment prior to analysis. Optical sensors provide an alternative approach for rapid and simple analysis of GHB samples. Unfortunately, currently reported probes are mostly based on hydrogen bonding to recognize GHB, and this raises concerns about, for example, the lack of specificity. In this work, we report a bioinspired strategy for selective sensing of GHB. The method is based on specific enzyme recognition to allow highly selective detection of GHB with minimum interference, even in a complex sample matrix (e. g., simulated urine). In addition, the result can be obtained by either quantitative spectroscopy analysis or colorimetric change observed by the naked-eye, thus demonstrating its potential application in drug screening and forensic analysis.

Designing dendronic-Raman markers for sensitive detection using surface-enhanced Raman spectroscopy

Surface-Enhanced Raman Spectroscopy (SERS) is well-established as a tool for bio-diagnostics but is often limited by analyte sensitivity and the need for specialized substrates. Signal enhancement can be achieved by attaching multiple Raman markers to a single analyte. Dendronic frameworks with multiple Raman markers attached to the periphery offer an opportunity to examine this idea. In this article, dendrons with thiophenol groups on their periphery were synthesized and tested as a SERS analyte. For this study, simple gold nanoparticles (∼60 nm) were used as a substrate. A 10² fold enhancement in detection was observed upon going from a mono-thiophenol (MT) to a tetra-thiophenol (TT). Dendronic Raman markers increased the probability of SERS occurrence at lower concentrations when compared to a single Raman active molecule. This strategy extends the applicability of SERS, as these analyte molecules can be just mixed or drop-casted on any kind of SERS substrate.

A new approach of tuning SERS enhancement with the aid of coupling chemistry for trace detection. A greater number of Raman-active molecules are constrained in a dendronic framework as an improved SERS analyte.

A Simple Colorimetric and Fluorescent Sensor to Detect Organophosphate Pesticides Based on Adenosine Triphosphate-Modified Gold Nanoparticles

A simple and dual modal (colorimetric and fluorescent) sensor for organophosphate pesticides with high sensitivity and selectivity using adenosine triphosphate (ATP)- and rhodamine B-modified gold nanoparticles (RB-AuNPs), was successfully fabricated. This detection for ethoprophos afforded colorimetric and fluorescence imaging changes visualization. The quantitative determination was linearly proportional to the amounts of ethoprophos in the range of a micromolar scale (4.0–15.0 µM). The limit of detection for ethoprophos was as low as 37.0 nM at 3σ/k. Moreover, the extent application of this simple assay was successfully demonstrated in tap water samples with high reliability and applicability, indicating remarkable application in real samples.

Detecting Biothreat Agents: From Current Diagnostics to Developing Sensor Technologies

Although a fundamental understanding of the pathogenicity of most biothreat agents has been elucidated and available treatments have increased substantially over the past decades, they still represent a significant public health threat in this age of (bio)terrorism, indiscriminate warfare, pollution, climate change, unchecked population growth, and globalization. The key step to almost all prevention, protection, prophylaxis, post-exposure treatment, and mitigation of any bioagent is early detection. Here, we review available methods for detecting bioagents including pathogenic bacteria and viruses along with their toxins. An introduction placing this subject in the historical context of previous naturally occurring outbreaks and efforts to weaponize selected agents is first provided along with definitions and relevant considerations. An overview of the detection technologies that find use in this endeavor along with how they provide data or transduce signal within a sensing configuration follows. Current "gold" standards for biothreat detection/diagnostics along with a listing of relevant FDA approved in vitro diagnostic devices is then discussed to provide an overview of the current state of the art. Given the 2014 outbreak of Ebola virus in Western Africa and the recent 2016 spread of Zika virus in the Americas, discussion of what constitutes a public health emergency and how new in vitro diagnostic devices are authorized for emergency use in the U.S. are also included. The majority of the Review is then subdivided around the sensing of bacterial, viral, and toxin biothreats with each including an overview of the major agents in that class, a detailed cross-section of different sensing methods in development based on assay format or analytical technique, and some discussion of related microfluidic lab-on-a-chip/point-of-care devices. Finally, an outlook is given on how this field will develop from the perspective of the biosensing technology itself and the new emerging threats they may face.

Enhanced Stability of Gold Magnetic Nanoparticles with Poly(4-styrenesulfonic acid-co-maleic acid): Tailored Optical Properties for Protein Detection

Gold magnetic nanoparticles (GoldMag) have attracted great attention due to their unique physical and chemical performances combining those of individual Fe₃O₄ and Au nanoparticles. Coating GoldMag with polymers not only increases the stability of the composite particles suspended in buffer but also plays a key role for establishing point-of-care optical tests for clinically relevant biomolecules. In the present paper, poly(4-styrenesulfonic acid-co-maleic acid) (PSS-MA), a negatively charged polyelectrolyte with both sulfonate and carboxylate anionic groups, was used to coat the positively charged GoldMag (30 nm) surface. The PSS-MA-coated GoldMag complex has a stable plasmon resonance adsorption peak at 544 nm. A pair of anti-D-dimer antibodies has been coupled on this GoldMag composite nanoparticle surface, and a target protein, D-dimer was detected, in the range of 0.3-6 μg/mL. The shift of the characteristic peak, caused by the assembly of GoldMag due to the formation of D-dimer-antibody sandwich bridges, allowed the detection.

Enzyme-responsive reporter molecules for selective localization and fluorescence imaging of pathogenic biofilms

A novel enzyme-responsive reporter molecule (ERM-1) for selective localization of AmpC in pathogenic biofilms.

Enzyme catalysis-electrophoresis titration for multiplex enzymatic assay via moving reaction boundary chip

In this work, we developed the concept of enzyme catalysis-electrophoresis titration (EC-ET) under ideal conditions, the theory of EC-ET for multiplex enzymatic assay (MEA), and a related method based on a moving reaction boundary (MRB) chip with a collateral channel and cell phone imaging. As a proof of principle, the model enzymes horseradish peroxidase (HRP), laccase and myeloperoxidase (MPO) were chosen for the tests of the EC-ET model. The experiments revealed that the EC-ET model could be achieved via coupling EC with ET within a MRB chip; particularly the MEA analyses of catalysis rate, maximum rate, activity, Km and Kcat could be conducted via a single run of the EC-ET chip, systemically demonstrating the validity of the EC-ET theory. Moreover, the developed method had these merits: (i) two orders of magnitude higher sensitivity than a fluorescence microplate reader, (ii) simplicity and low cost, and (iii) fairly rapid (30 min incubation, 20 s imaging) analysis, fair stability (<5.0% RSD) and accuracy, thus validating the EC-ET method. Finally, the developed EC-ET method was used for the clinical assay of MPO activity in blood samples; the values of MPO activity detected via the EC-ET chip were in agreement with those obtained by a traditional fluorescence microplate reader, indicating the applicability of the EC-ET method. The work opens a window for the development of enzymatic research, enzyme assay, immunoassay, and point-of-care testing as well as titration, one of the oldest methods of analysis, based on a simple chip.

Stimuli-Responsive Extraction and Ambidextrous Redispersion of Zwitterionic Amphiphile-Capped Silver Nanoparticles

Citrate-stabilized silver nanoparticles (AgNPs) were functionalized with a pH-responsive amphiphile, 3-[(2-carboxy-ethyl)-hexadecyl-amino]-propionic acid (C16CA). At pH ∼ 4, the zwitterionic C16CA assembled into lamellar structures due to the protonation of the amine groups of the amphiphile that neutralized the anionic charge of the carboxylate groups. The lamellar supramolecules incorporated the AgNPs into their 3D network and extracted them from water. C16CA supramolecules dissolved into water (at pH > 6) and organic solvents; consequently, the recovered C16CA-AgNPs were redispersed not only to water but also to chloroform and tetrahydrofuran without any additional functionalization. C16CA acted as a pH-responsive stabilizer of AgNPs and formed a solvent-switchable molecular layer such as a bilayered structure in water and densely packed monolayer in chloroform and tetrahydrofuran. Redispersion of the AgNPs was achieved in different solvents by changing the solvent affinity of the adsorbed C16CA molecular layer based on the protonation of the amine groups of the pH-responsive amphiphile. The morphology of redispersed AgNPs did not change during the recovery and redispersion procedure, due to the high steric effect of the network structure of C16CA supramolecules. These observations can lead to a novel solvent-exchange method for nanocrystals without aggregation and loss of nanocrystals, and they enable effective preparations of stimuli-responsive plasmonic nanomaterials.

Dual Reaction-Based Multimodal Assay for Dopamine with High Sensitivity and Selectivity Using Functionalized Gold Nanoparticles

A simple and dual chemical reaction-based multimodal assay for dopamine with high sensitivity and selectivity using two types of functionalized gold nanoparticles (FB-AuNPs/NsNHS-AuNPs), i.e. fluorescein modified gold nanoparticles (FB-AuNPs) and Nile blue modified gold nanoparticles (NsNHS-AuNPs), was successfully fabricated. This assay for dopamine presents colorimetric visualization and double channel fluorescence enhancement at 515 and 665 nm. The absorbance and fluorescence changes were linearly proportional to the amounts of dopamine in the range of nanomolar scale (5-100 nM). The detection limits for absorbance and fluorescence were as low as 1.2 nM and 2.9 nM (S/N = 3), respectively. Furthermore, the extent application of this multimodal assay has been successfully demonstrated in human urine samples with high reliability and applicability, showing remarkable promise in diagnostic purposes.

Colorimetric biosensing of pathogens using gold nanoparticles

Rapid detection of pathogens is crucial to minimize adverse health impacts of nosocomial, foodborne, and waterborne diseases. Gold nanoparticles are extremely successful at detecting pathogens due to their ability to provide a simple and rapid color change when their environment is altered. Here, we review general strategies of implementing gold nanoparticles in colorimetric biosensors. First, we highlight how gold nanoparticles have improved conventional genomic analysis methods by lowering detection limits while reducing assay times. Then, we focus on emerging point-of-care technologies that aim at pathogen detection using simpler assays. These advances will facilitate the implementation of gold nanoparticle-based biosensors in diverse environments throughout the world and help prevent the spread of infectious diseases.

pH-induced recovery and redispersion of shape-controlled gold nanorods for nanocatalysis

The pH-responsive amphiphile C16CA was used for the functionalization of gold nanorods. The pH-induced recovery–redispersion of gold nanorods using C16CA self-assembly was accomplished without affecting the catalytic activity of the nanorods.

Visual detection of hexokinase activity and inhibition with positively charged gold nanoparticles as colorimetric probes

Positively charged gold nanoparticles can effectively differentiate ATP and ADP, thus providing a simple and visual approach to colorimetric detection of hexokinase activity and inhibition.

Polyelectrolyte-coated gold magnetic nanoparticles for immunoassay development: toward point of care diagnostics for syphilis screening

Immediate response for disease control relies on simple, inexpensive, and sensitive diagnostic tests, highly sought after for timely and accurate test of various diseases, including infectious diseases. Composite Fe3O4/Au nanoparticles have attracted considerable interest in diagnostic applications due to their unique physical and chemical properties. Here, we developed a simple coating procedure for gold magnetic nanoparticles (GMNs) with poly(acrylic acid) (PAA). PAA-coated GMNs (PGMNs) were stable and monodispersed and characterized by Fourier transform-infrared spectroscopy (FT-IR), transmission electron microscopy, UV-visible scanning spectrophotometry, thermogravimetric analysis, and Zetasizer methodologies. For diagnostic application, we established a novel lateral flow immunoassay (LFIA) strip test system where recombinant Treponema pallidum antigens (r-Tp) were conjugated with PGMNs to construct a particle probe for detection of anti-Tp antibodies. Intriguingly, the particle probes specifically identified Tp antibodies with a detection limitation as low as 1 national clinical unit/mL (NCU/mL). An ample pool of 1020 sera samples from three independent hospitals were obtained to assess our PGMNs-based LFIA strips, which exhibited substantially high values of sensitivity and specificity for all clinical tests (higher than 97%) and, therefore, proved to be a suitable approach for syphilis screening at a point-of-care test manner.

Enzyme responsive materials: design strategies and future developments

Enzyme responsive materials (ERMs) are a class of stimuli responsive materials with broad application potential in biological settings. This review highlights current and potential future design strategies for ERMs and provides an overview of the present state of the art in the area.

Lipopolysaccharide neutralizing peptide-porphyrin conjugates for effective photoinactivation and intracellular imaging of gram-negative bacteria strains

A simple and specific strategy based on the bioconjugation of a photosensitizer protophophyrin IX (PpIX) with a lipopolysaccharide (LPS) binding antimicrobial peptide YI13WF (YVLWKRKRKFCFI-Amide) has been developed for the effective fluorescent imaging and photodynamic inactivation of Gram-negative bacterial strains. The intracellular fluorescent imaging and photodynamic antimicrobial chemotherapy (PACT) studies supported our hypothesis that the PpIX-YI13WF conjugates could serve as efficient probes to image the bacterial strains and meanwhile indicated the potent activities against Gram-negative bacterial pathogens especially for those with antibiotics resistance when exposed to the white light irradiation. Compared to the monomeric PpIX-YI13WF conjugate, the dimeric conjugate indicated the stronger fluorescent imaging signals and higher photoinactivation toward the Gram-negative bacterial pathogens throughout the whole concentration range. In addition, the photodynamic bacterial inactivation also demonstrated more potent activity than the minimum inhibitory concentration (MIC) values of dimeric PpIX-YI13WF conjugate itself observed for E. coli DH5a (~4 times), S. enterica (~8 times), and other Gram-negative strains including antibiotic-resistant E. coli BL21 (~8 times) and K. pneumoniae (~16 times). Moreover, both fluorescent imaging and photoinactivation measurements also demonstrated that the dimeric PpIX-YI13WF conjugate could selectively recognize bacterial strains over mammalian cells and generate less photo damage to mammalian cells. We believed that the enhanced fluorescence and bacterial inactivation were probably attributed to the higher binding affinity between dimeric photosensitizer peptide conjugate and LPS components on the surface of bacterial strains, which were the results of efficient multivalent interactions.

Sensitive colorimetric visualization of dihydronicotinamide adenine dinucleotide based on anti-aggregation of gold nanoparticles via boronic acid-diol binding

A facile, highly sensitive colorimetric strategy for dihydronicotinamide adenine dinucleotide (NADH) detection is proposed based on anti-aggregation of gold nanoparticles (AuNPs) via boronic acid-diol binding chemistry. The aggregation agent, 4-mercaptophenylboronic acid (MPBA), has specific affinity for AuNPs through Au-S interaction, leading to the aggregation of AuNPs by self-dehydration condensation at a certain concentration, which is responsible for a visible color change of AuNPs from wine red to blue. With the addition of NADH, MPBA would prefer reacting with NADH to form stable borate ester via boronic acid-diol binding dependent on the pH and solvent, revealing an obvious color change from blue to red with increasing the concentration of NADH. The anti-aggregation effect of NADH on AuNPs was seen by the naked eye and monitored by UV-vis extinction spectra. The linear range of the colorimetric sensor for NADH is from 8.0 × 10(-9)M to 8.0 × 10(-6)M, with a low detection limit of 2.0 nM. The as-established colorimetric strategy opened a new avenue for NADH determination.

Nanoprobes for in vitro diagnostics of cancer and infectious diseases

The successful and explosive development of nanotechnology is significantly impacting the fields of biology and medicine. Among the spectacular developments of nanobiotechnology, interest has grown in the use of nanomaterials as nanoprobes for bioanalysis and diagnosis. Herein, we review state-of-the-art nanomaterial-based probes and discuss their applications in in vitro diagnostics (IVD) and challenges in bringing these fields together. Major classes of nanoprobes include quantum dots (QDs), plasmonic nanoparticles, magnetic nanoparticles, nanotubes, nanowires, and multifunctional nanomaterials. With the advantages of high volume/surface ratio, surface tailorability, multifunctionality, and intrinsic properties, nanoprobes have tremendous applications in the areas of biomarker discovery, diagnostics of infectious diseases, and cancer detection. The distinguishing features of nanoprobes for in vitro use, such as harmlessness, ultrasensitivity, multiplicity, and point-of-care use, will bring a bright future of nanodiagnosis.

Colourimetric and spectroscopic discrimination between nucleotides and nucleosides using para-sulfonato-calix[4]arene capped silver nanoparticles

The complexation of nucleosides and nucleotides by hybrid nanoparticles capped by para-sulfonato-calix[4]arene shows clear discrimination between purine and pyrimidine based molecules. For the pyrimidine nucleotides there is appearance of a new absorption band around 550 nm, and a colour change from yellow to orange red and pink.

Dual-signal fenamithion probe by combining fluorescence with colorimetry based on Rhodamine B modified silver nanoparticles

A versatile yet simple strategy for the fabrication of a highly selective and sensitive fenamithion probe based on Rhodamine B (RB) modified silver nanoparticles (RB-Ag NPs) was developed. The advantage of our system over classical assays is that it combined fluorescence with colorimetry which can realize the prompt on-site and real-time detection of fenamithion with high sensitivity (0.1 nM) in aqueous solution. Moreover, the detection system presents excellent anti-disturbance ability when exposed to a series of interfering ionic/pesticides mixtures and can be applied to the determination of fenamithion in real vegetables and different water samples with the limit of detection (LOD) as low as 10 nM (0.0026 mg L(-1)), which is in accord with the maximum contamination level of 0.001∼0.25 mg L(-1) for organophosphorus pesticides as defined by the U.S. Environmental Protection Agency (EPA). Advantage is taken of the fact that RB would be displaced from the surface of the Ag NPs because of the stronger coordination ability of Ag NPs with fenamithion, an amino-containing organophosphorus pesticide, accompanying the clustered Ag NPs (9 nm) dissipating into smaller individual particles (7 nm). Based on this phenomenon, a novel analyte-induced etching mechanism was proposed.

Peptide-tailored assembling of Aunanorods

A simple and fast way to study the interaction between the Au NRs and peptides was developed, which makes potential peptide recognition and detection possible.

Single gold nanoparticles counter: an ultrasensitive detection platform for one-step homogeneous immunoassays and DNA hybridization assays

In this paper, we present for the first time a single gold nanoparticle counter (SGNPC) in solution based on the photon bursting in a highly focused laser beam (less than 1 fL) due to the plasmon resonance scattering and Brownian motion of gold nanoparticles (GNPs). The photon burst intensity of single 36 nm GNPs is several tens to hundreds times stronger than that of quantum dots (QDs) and organic dyes. The relationship between the photon burst counts and GNPs concentration shows an excellent linearity. The linear range is over 4 orders of magnitude, and the detection limit of GNPs (36 nm) is 17 fM. On the basis of this single nanoparticle technique, we developed an ultrasensitive and highly selective detection platform for homogeneous immunoassay and DNA hybridization assays using GNPs as probes, which were 2-5 orders of magnitude more sensitive than current homogeneous methods. We used this technology to construct homogeneous sandwich immunoassays for cancer biomarkers, such as carcinoembryonic antigen (CEA) and alpha fetal protein (AFP), and aptamer recognition for thrombin. The detection limits are 130 fM for CEA, 714 fM for AFP and 2.72 pM for thrombin. Our method was successfully applied for direct determination of CEA, AFP and thrombin levels in sera from healthy subjects and cancer patients. In homogeneous DNA hybridization detection, we chose methylenetetrahydrofolate reductase (MTHFR) gene as a target. This assay successfully distinguished DNA sequences with single base mismatches, and the detection limits for the target were at 1 fM level.