A Simple Colorimetric Analytical Assay for the Determination of Tetracyclines Based on In-situ Generation of Gold Nanoparticles Coupling with a Gold Staining Technique

The development of simple and sensitive detection methods for tetracyclines (TCs) is crucial for their routine detection. The present study developed a colorimetric method for the detection of TCs based on the in-situ generation of AuNPs, which were subsequently coupled with a gold staining reaction. Briefly, TCs containing phenolic groups reduce HAuCl₄ to form gold nanoparticles (AuNPs) as gold seeds. In the gold staining process, the gold seeds catalyze the reduction of HAuCl₄ by NH₂OH to form gold atoms that deposit on the surface of AuNPs, resulting in the enlargement of AuNPs. Sensitive detection of TCs was achieved by employing the gold staining technique. As low as 14, 18.9, and 1.98 nM of oxytetracycline (OTC), tetracycline (TC), and doxycycline (DC), respectively, could be sensitively detected. The proposed method also exhibited good repeatability and specificity, and then was applied to the determination of OTC in milk samples.

A cascade amplification strategy based on rolling circle amplification and hydroxylamine amplified gold nanoparticles enables chemiluminescence detection of adenosine triphosphate

A highly sensitive and selective chemiluminescent (CL) biosensor for adenosine triphosphate (ATP) was developed by taking advantage of the ATP-dependent enzymatic reaction (ATP-DER), the powerful signal amplification capability of rolling circle amplification (RCA), and hydroxylamine-amplified gold nanoparticles (Au NPs). The strategy relies on the ability of ATP, a cofactor of T4 DNA ligase, to trigger the ligation-RCA reaction. In the presence of ATP, the T4 DNA ligase catalyzes the ligation reaction between the two ends of the padlock probe, producing a closed circular DNA template that initiates the RCA reaction with phi29 DNA polymerase and dNTP. Therein, many complementary copies of the circular template can be generated. The ATP-DER is eventually converted into a detectable CL signal after a series of processes, including gold probe hybridization, hydroxylamine amplification, and oxidative gold metal dissolution coupled with a simple and sensitive luminol CL reaction. The CL signal is directly proportional to the ATP level. The results showed that the detection limit of the assay is 100 pM of ATP, which compares favorably with those of other ATP detection techniques. In addition, by taking advantage of ATP-DER, the proposed CL sensing system exhibits extraordinary specificity towards ATP and could distinguish the target molecule ATP from its analogues. The proposed method provides a new and versatile platform for the design of novel DNA ligation reaction-based CL sensing systems for other cofactors. This novel ATP-DER based CL sensing system may find wide applications in clinical diagnosis as well as in environmental and biomedical fields.

Controlled growth of immunogold for amplified optical detection of aflatoxin B1

A simple, sensitive and cost-effective method for the analysis of the mycotoxin aflatoxin B1 (AFB1) has been established based on controlled growth of immunogold.

Hydroxylamine amplified gold nanoparticle-based aptameric system for the highly selective and sensitive detection of platelet-derived growth factor

This study developed a sensitive and selective aptamer-based chemiluminescent (CL) method for the determination of platelet-derived growth factor (PDGF)-BB using hydroxylamine enlarged gold nanoparticles (Au NPs). Rabbit anti-human PDGF-BB polyclonal antibody was covalently coupled on the 96-well plate that offers reactive N-oxysuccinimide ester (referred to as NOS group) surface. In the presence of target protein, the biotinylated aptamer was captured on the 96-well plate forming an antibody/PDGF-BB/biotinylated aptamer sandwiched complex, which was followed by the assembly of streptavidin coated Au NPs (streptavidin-gold). Au NPs assembled on the surface of 96-well plate reacted with HAuCl(4) and NH(2)OH, which enabled the catalytic deposition of gold metal onto the Au NPs surfaces. A huge number of Au(3+) ions were released from the hydroxylamine enlarged Au NPs after oxidative gold metal dissolution, which was determined by a simple and sensitive luminol CL reaction. The results showed that the detection limit of the assay is 60 pM of PDGF-BB (corresponding to 6 fmol in a 100 μL volume), which compares favorably with those of other PDGF-BB detection techniques. In addition, this aptameric CL biosensor demonstrated extraordinary specificity. And PDGF-BB has been determined in diluted serum indicating the applicability of this assay.

Electrical immunosensor based on a submicron-gap interdigitated electrode and gold enhancement

We demonstrated that the detection of human interleukin 5 (IL5) with a higher sensitivity than the enzyme-linked immunosorbent assay (ELISA) was possible using mass-producible submicron-gap interdigitated electrodes (IDEs) combined with signal amplification by a gold nanoparticle (AuNP) and gold enhancement. IDEs, facing comb-shape electrodes, can act as simple and miniaturized devices for immunoassay. An IDE with a gap size of 400nm was fabricated by a stepper photolithography process and was applied for the immunoassay of human IL5. A biotinylated anti-human IL5 was immobilized on the streptavidin-modified IDE, and biotin-bovine serum albumin (BSA) and BSA were added sequentially to reduce non-specific binding between the streptavidin-immobilized IDE surface and other proteins. The immunoassay procedure included three main steps: the reaction of human IL5 to form antigen-antibody complexes, the binding of AuNP conjugation with an antibody against human IL5 for the sandwich immunoassay, and gold enhancement for electrical signal amplification. The measurement of electrical current at each step showed that the gold enhancement step was very critical in detection of the concentration of human IL5. Analysis by scanning electron microscope (SEM) showed that close to 1μm particles were formed from 10nm AuNP by the gold enhancement reaction using gold ions and hydroxylamine. Under optimized conditions, human IL5 could be analyzed at 1pgmL(-1) with a wide dynamic range (from 10(-3) to 100ngmL(-1) concentrations).

Hydroxylamine-amplified gold nanoparticles for the homogeneous detection of sequence-specific DNA

Herein, we report the development of a simple, sensitive, inexpensive, and homogeneous detection method for the analysis of DNA hybridization based on the optical properties of hydroxylamine-amplified gold nanoparticles (Au NPs) in solution phase. The assay relies on a sandwich-type DNA hybridization in which DNA targets are first hybridized with capture DNA probes immobilized on the surface of magnetic beads and then sandwiched with Au NPs modified with biotinylated reporter DNA. Au NPs, after being anchored on the magnetic beads, are then dispersed in solution by the dehybridization and enlarged by using a mixture of HAuCl(4) and NH(2)OH. The Au NP growth signal which is used for the quantitative analysis of sequence-specific DNA can be easily monitored by the naked eye directly or an UV-vis spectrophotometer. Surface plasmonic signature of the enlarged Au NPs and the kinetics of the Au NP growth in the homogenous phase containing of HAuCl(4) and NH(2)OH have also been studied. As a result, such a homogeneous assay allows the detection of 30-base DNA targets down to the 100 amol level, which offers great promise for facilitating sensitive detection of other biorecognition events.