Choiwan Lau

Turn-On Chemiluminescence Sensor for the Highly Selective and Ultrasensitive Detection of Hg2+ Ions Based on Interstrand Cooperative Coordination and Catalytic Formation of Gold Nanoparticles

Monitoring the levels of potentially toxic metal ions such as Hg(2+) in aquatic ecosystems is important because this ion can have severe effects on human health and the environment. Thus, a novel chemiluminescence (CL) sensor is developed for the highly selective and ultrasensitive detection of Hg(2+) ions in aqueous solution, based on thymine-Hg(2+)-thymine (T-Hg(2+)-T) coordination chemistry and subsequent formation of gold nanoparticles (Au NPs) in a HAuCl(4)/NH(2)OH reaction. The thus-formed Au NPs trigger the reaction between luminol and AgNO(3), producing CL emission. This novel CL technique has several advantages including high sensitivity (0.01 ppb) and selectivity over a spectrum of interfering metal ions. In view of these advantages, as well as the cost-effective, minimized working steps and portable features of the CL techniques, we expect that this CL sensor will be a promising candidate for the field detection of toxic Hg(2+) ions in environment, water, and food samples.

Instantaneous derivatization technology for simultaneous and homogeneous determination of multiple DNA targets.

There are potential advantages, in terms of simplicity and speed, for detecting DNA hybridization steps directly without using any external labels, especially for the multiplexed assays. In the current paper, we describe the use of a carrier-resolved label-free multiplexed assay for the simultaneous detection of multiple DNA targets. Herein we demonstrate that this protocol, using three homogeneous carriers thermosensitive poly(N-isopropylacrylamide), polystyrene beads, and magnetic beads, respectively, for simultaneous determination of three short DNA fragments specific to hepatitis B virus. Briefly, one hybridization occurs between a mixture of three different capture probe DNAs immobilized onto three carriers and three targets in a single vessel, and then chemiluminescence (CL) detection proceeds via an instantaneous derivatization reaction between the specific CL reagent 3,4,5-trimethoxylphenylglyoxal (TMPG) and the guanine nucleotide-rich regions within the target DNA. An excellent linearity is found within the range between 0.1 and 6.0 pmol with the lowest detection limit of 100 fmol. In contrast to current encoding strategies, every hybridization signal for the corresponding DNA target in our protocol is uniquely immobilized onto one carrier vehicle with a unique and intrinsic physical-chemical signature. Moreover, an instantaneous derivatization reaction is employed for the label-free determination of three targets in a single vessel. In addition, a simple CL setup is employed to read the carrier code instead of an expensive and complicated flow cytometer or imaging system commonly used for multiplexed assays. Further signal amplification is achieved by employing three amplified DNAs for second hybridization, which include a guanine nucleobase-rich sequence domain for the generation of light and an additional tethered nucleic acid domain complementary with one of the target DNA as an amplification platform. Such simple amplified CL transduction allows detection of DNA targets down to the 15-fmol level. This new protocol also provided a good capability in discriminating perfectly complementary DNA from single-base mismatches and noncomplementary sequences. Overall, the protocol described here may have value in a variety of clinical, environmental, and biodefense applications for which the accurate quantitative analysis of multiple DNA targets is desired.

Sequence-specific detection of short-length DNA via template-dependent surface-hybridization events.

Short-length DNA and RNA, such as mature small RNA, which contains only 17-25 nucleotides, are always a problem in hybridization-based detection assays. In this paper, we report a proof-of-concept for a new short-length DNA detection technology which encompasses a design strategy whereby capture and reporter probes that do not hybridize to each other at 20 degrees C can be made to anneal to each other in the presence of a template via the formation of a stable three-component complex. The thermodynamics of this magnetic bead-based DNA biosensor was then investigated in detail by monitoring chemiluminescence (CL) changes in the absence and presence of targets over a temperature profile. The data show that this new biosensor offers the possibility of highly selective and sensitive detection of the short-length target DNA. In view of these advantages, this template-dependent surface-hybridization assay, as a new CL strategy, might create a universal technology for developing simple biosensors in sensitive and selective detection of short-length DNA and RNA.

Direct colorimetric visualization of mercury (Hg2+) based on the formation of gold nanoparticles

It is critical to be able to detect and quantify Hg(2+) ions under aqueous conditions with high sensitivity and selectivity. The technique presented herein provides a direct way for simple colorimetric visualization of Hg(2+) ions in aqueous solution, based on the formation of gold nanoparticles through the Hg(2+) catalyzed HAuCl(4)/NH(2)OH reaction. The outstanding selectivity and sensitivity result from the well-known amalgamation process that occurs between mercury and gold. The entire procedure takes less than 20 min. The limit of detection (2 ppb) shows excellent potential for monitoring ultralow levels of mercury in water samples.

Hybridization chain reaction-based aptameric system for the highly selective and sensitive detection of protein

We introduce here a novel assay for the detection of platelet-derived growth factor BB (PDGF-BB) via hybridization chain reaction (HCR) based on an aptameric system, where stable DNA monomers assemble only upon exposure to a target PDGF-BB aptamer. In this process, two complementary stable species of biotinylated DNA hairpins coexist in solution until the introduction of initiator aptamer strands triggers a cascade of hybridization events that yields nicked double helices analogous to alternating copolymers. In detail, the aptamer firstly opens the hairpins in the solution, creating long concatemers, and then reacts with the antibody captured PDGF-BB on the well surface. Moreover, several experimental conditions including different PDGF-BB aptamers, the spacer length of the selected aptamer and hairpin, etc. are investigated and optimized. Our results show that the coupling of HCR to aptamer triggers for the amplification detection of PDGF-BB achieves a better performance in the fluorescence detection of PDGF-BB as compared to the traditional antibody-antigen-aptamer assays. Upon modification, the approach presented herein could be extended to detect other types of targets. We believe such advancements will represent a significant step towards improved diagnostics and more personalized medical treatment and environmental monitoring.

Cross-talk-free simultaneous fluoroimmunoassay of two biomarkers based on dual-color quantum dots.

In this article, we demonstrate the fabrication and simultaneous fluorescent detection of two biomarkers related to lung cancer. Polystyrene microspheres (PSM) were introduced as biomolecular immobilizing carriers and a 96-well filter plate was used as the separation platform. The whole experiment could be effectively carried out in a homogeneous system, as exemplified by the detection of carcinoembryonic antigen (CEA) and neuron specific enolase (NSE). First, two capture antibodies for CEA and NSE were immobilized on the PSM surface. Next, they reacted successively with two antigens and two modified detection antibodies. Finally, these two biomarkers could be recognized by streptavidin-conjugated quantum dots (QD) and goat-anti-FITC conjugated QD with a detection limit of 0.625 ng mL(-1), which was lower than the clinical cut-off level. The protocol showed good precision within 6.36% and good recovery in the range of 90.86-105.02%. Compared with several other assay formats reported previously, our new technique is competitive or even better. Furthermore, the immunosensor was successfully illustrated in 20 serum samples. Overall, this new immunoassay offers a promising alternative for the detection of biomarkers related to cancer diseases, taking advantage of simplicity, specificity, sensitivity and cost-efficiency.

A simple and sensitive chemiluminescence method for the determination of tiopronin for a pharmaceutical formulation

Here we report a rather simple and convenient chemiluminescence (CL) method for the determination of tiopronin. It was based that tiopronin could greatly enhance CL between H2O2 and luminol in a basic alkaline solution. Light emission is intense, and even with a simple setup a high sensitivity could be achieved. The linear range was 3 mM-500 nM with a detection limit of 200 nM. Singlet oxygen and hydroxyl radical were suggested to be produced in this reaction and was responsible for the CL of tiopronin. As a preliminary application, this simple method has been successfully applied into the determination of tiopronin in a pharmaceutical formulation.

Combination of quantum dot fluorescence with enzyme chemiluminescence for multiplexed detection of lung cancer biomarkers

A new concept is proposed in this article to detect multiple cancer markers in a single sample. Quantum dot (QD) fluorescence (FL) labels were successfully combined with enzyme chemiluminescence (CL) labels for simultaneous detection of three cancer markers in human serum using just a common 96-well plate reader and with equal detection limits for the three markers. As a proof-of-concept, herein we coupled one QD FL label with two enzyme CL labels for hybrid multiplexed detection of lung cancer markers as exemplified by neuron-specific enolase (NSE), carcinoembryonic antigen (CEA) and cytokeratin fragment (Cyfra21-1). A homogeneous “sandwich-type” detection strategy was employed herein, where the bead–antibody mixture first reacts with NSE, CEA and Cyfra21-1 to initiate three immunoreactions in a single tube; and then the formed conjugates sandwiches with biotin, digoxin and fluoresceinisothiocyanate (FITC)-modified detection antibodies, and further reacts with a mixture of streptavidin QD, anti-FITC horseradish peroxidase (HRP) and anti-digoxin alkaline phosphatase (ALP) for subsequent CL and FL detection. The results show that NSE, CEA and Cyfra21-1 could be sensitively determined with a common 96-well plate reader and with equal detection limits down to the ng mL−1 level. Furthermore, the proposed method has been successfully applied to the determination of three cancer markers in human samples without cross-reaction. Because it is straightforward to adapt this strategy to detect a spectrum of other proteins by using different antibodies or aptamers, this new CL strategy might create a universal technology for developing simple biosensors in the sensitive and selective detection of multiple targets in a variety of clinical, environmental, and biodefense applications.

Turn-on aptameric system for simple and selective detection of protein via base stacking-dependent DNA hybridization event.

Base stacking is employed in an entirely new type of sensing platform for the simple and robust detection of protein. Only in the presence of protein, the aptamer DNA can hybridize stably with the capture DNA to form a stem-loop structure due to the enhancement of base stacking. This leads to a strong chemiluminescence emission for simple protein detection. With the use of a platelet-derived growth factor as a model, a fM detection limit was obtained with a dynamic range that spanned 4 orders of magnitude. Upon modification, the approach presented herein was also extended to detect other types of targets including Hg(2+) ion and adenosine and also other types of labels such as fluorescence nanogold. We believe such advancements will represent a significant step toward improved diagnostics and more personalized medical treatment and environmental monitoring.

A general chemiluminescence method for the determination of surfactants based on its quenching effect on the luminol-NaIO4-cyclodextrin reaction.

Here we report that all types of surfactant could be simply and sensitively determined, by directly quenching the chemiluminescence (CL) between luminol and NaIO4 in a basic solution containing one polyhydroxyl compound such as cyclodextrin (CD), glucose or glycerol. This specific quenching effect was attributed to the change of the microenvironment of the CL reaction, caused by the addition of various surfactants. Based on this fact, the potential use of this CL reaction was exemplified by the cationic surfactant CTMAB, anionic surfactant SDS and non-ionic surfactant Triton X-100. It was found that the measurable range of CTMAB, SDS and Triton X-100 were 4.0 x 10(-6)-4.0 x 10(-4) M by using a basic CD-luminol-NaIO4 CL reaction. With our simple setup, CTMAB, SDS and Triton X-100 were detectable at a concentration as low as 2 microM. Overall, this new CL reaction is quite promising for the post-column determination of surfactant mixtures.