Shuangyan Huan

A nano-Ni based ultrasensitive nonenzymatic electrochemical sensor for glucose: enhancing sensitivity through a nanowire array strategy.

Highly ordered Ni nanowire arrays (NiNWAs) were synthesized for the first time using a template-directed electropolymerization strategy with a nanopore polycarbonate (PC) membrane template, and their morphological characterization were examined by scanning electron microscopy (SEM) and transmission electron microscope (TEM). A NiNWAs based electrode shows very high electrochemical activity for electrocatalytic oxidation of glucose in alkaline medium, which has been utilized as the basis of the fabrication of a nonenzymatic biosensor for electrochemical detection of glucose. The biosensor can be applied to the quantification of glucose with a linear range covering from 5.0x10(-7) to 7.0x10(-3) M, a high sensitivity of 1043 microA mM(-1) cm(-2), and a low detection limit of 1x10(-7) M. The experiment results also showed that the sensor exhibits good reproducibility and long-term stability, as well as high selectivity with no interference from other oxidable species.

Naphthalimide−Porphyrin Hybrid Based Ratiometric Bioimaging Probe for Hg2+: Well-Resolved Emission Spectra and Unique Specificity

In this paper, we unveil a novel naphthalimide-porphyrin hybrid based fluorescence probe (1) for ratiometric detection of Hg(2+) in aqueous solution and living cells. The ratiometric signal change of the probe is based on a carefully predesigned molecule containing two independent Hg(2+)-sensitive fluorophores with their maximal excitation wavelengths located at the same range, which shows reversibly specific ratiometric fluorescence responses induced by Hg(2+). In the new developed sensing system, the emissions of the two fluorophores are well-resolved with a 125 nm difference between two emission maxima, which can avoid the emission spectra overlap problem generally met by spectra-shift type probes and is especially favorable for ratiometric imaging intracellular Hg(2+). It also benefits from a large range of emission ratios and thereby a high sensitivity for Hg(2+) detection. Under optimized experimental conditions, the probe exhibits a stable response for Hg(2+) over a concentration range from 1.0 x 10(-7) to 5.0 x 10(-5) M, with a detection limit of 2.0 x 10(-8) M. The response of the probe toward Hg(2+) is reversible and fast (response time less than 2 min). Most importantly, the ratiometric fluorescence changes of the probe are remarkably specific for Hg(2+) in the presence of other abundant cellular metal ions (i.e., Na(+), K(+), Mg(2+), and Ca(2+)), essential transition metal ions in cells (such as Zn(2+), Fe(3+), Fe(2+), Cu(2+), Mn(2+), Co(2+), and Ni(2+)), and environmentally relevant heavy metal ions (Ag(+), Pb(2+), Cr(3+), and Cd(2+)), which meets the selective requirements for biomedical and environmental monitoring application. The recovery test of Hg(2+) in real water samples demonstrates the feasibility of the designed sensing system for Hg(2+) assay in practical samples. It has also been used for ratiometric imaging of Hg(2+) in living cells with satisfying resolution, which indicates that our novel designed probe has effectively avoided the general emission spectra overlap problem of other ratiometric probes.

Translating Bacterial Detection by DNAzymes into a Litmus Test

Microbial pathogens pose serious threats to public health and safety, and results in millions of illnesses and deaths as well as huge economic losses annually. Laborious and expensive pathogen tests often represent a significant hindrance to implementing effective front-line preventative care, particularly in resource-limited regions. Thus, there is a significant need to develop low-cost and easy-to-use methods for pathogen detection. Herein, we present a simple and inexpensive litmus test for bacterial detection. The method takes advantage of a bacteria-specific RNA-cleaving DNAzyme probe as the molecular recognition element and the ability of urease to hydrolyze urea and elevate the pH value of the test solution. By coupling urease to the DNAzyme on magnetic beads, the detection of bacteria is translated into a pH increase, which can be readily detected using a litmus dye or pH paper. The simplicity, low cost, and broad adaptability make this litmus test attractive for field applications, particularly in the developing world.

Multicolor fluorescent biosensor for multiplexed detection of DNA.

Development of efficient methods for highly sensitive and rapid screening of specific oligonucleotide sequences is essential to the early diagnosis of serious diseases. In this work, an aggregated cationic perylene diimide (PDI) derivative was found to efficiently quench the fluorescence emission of a variety of anionic oligonucleotide-labeled fluorophores that emit at wavelengths from the visible to NIR region. This broad-spectrum quencher was then adopted to develop a multicolor biosensor via a label-free approach for multiplexed fluorescent detection of DNA. The aggregated perylene derivative exhibits a very high quenching efficiency on all ssDNA-labeled dyes associated with biosensor detection, having efficiency values of 98.3 ± 0.9%, 97 ± 1.1%, and 98.2 ± 0.6% for FAM, TAMRA, and Cy5, respectively. An exonuclease-assisted autocatalytic target recycling amplification was also integrated into the sensing system. High quenching efficiency combined with autocatalytic target recycling amplification afforded the biosensor with high sensitivity toward target DNA, resulting in a detection limit of 20 pM, which is about 50-fold lower than that of traditional unamplified homogeneous fluorescent assay methods. The quencher did not interfere with the catalytic activity of nuclease, and the biosensor could be manipulated in either preaddition or postaddition manner with similar sensitivity. Moreover, the proposed sensing system allows for simultaneous and multicolor analysis of several oligonucleotides in homogeneous solution, demonstrating its potential application in the rapid screening of multiple biotargets.

Surface-Enhanced Raman Spectroscopic Detection of a Bacteria Biomarker Using Gold Nanoparticle Immobilized Substrates

The development of ultrasensitive and rapid methods for the detection of dipicolinic acid (DPA), a biomarker for bacterial spores including Bacillus anthracis, is increasingly important. This paper reports the results of an investigation of surface enhanced Raman spectroscopy (SERS) based ultrasensitive detection of DPA using a gold nanoparticle/polyvinylpyrrolidone/gold substrate (AuNPs/PVP/Au). The strong SERS effect of this substrate exploits the particle-particle and particle-substrate plasmonic coupling, which is optimized by manipulating the diameter of the nanoparticles (50-70 nm). The correlation between the SERS intensity of the diagnostic band and the DPA concentration (0.1 ppb to 100 ppm) was shown to exhibit two linear regions, i.e., the low- (<0.01 ppm) and high-concentration (>1 ppm) regions, with an intermediate region in between. The presence of a linear relationship in the low-concentration region was observed for the first time in SERS detection of DPA. A detection limit of 0.1 ppb was obtained from the substrates with 60 nm sized Au NPs, which is, to our knowledge, the lowest detection limit reported for DPA using this type of SERS substrate. This finding was also supported by the estimated enhancement factor (approximately 10(6)) and a large adsorption equilibrium constant for the low-concentration region (1.7 x 10(7) M(-1)). The adsorption characteristics of DPA on the SERS substrates were analyzed in terms of monolayer and multilayer adsorption isotherms to gain insights into the correlation between the SERS intensity and the DPA concentration. The observed transition from the low- to high-concentration linear regions was found to correspond to the transition from a monolayer to multilayer adsorption isotherm, which was in agreement with the estimated minimum DPA concentration for a monolayer coverage (approximately 0.01 ppm).

Nanoparticle-based substrates for surface-enhanced Raman scattering detection of bacterial spores

The development of ultrasensitive and rapid methods for the detection of bacterial spores is important for medical diagnostics of infectious diseases. While Surface-Enhanced Raman Spectroscopic (SERS) techniques have been increasingly demonstrated for achieving this goal, a key challenge is the development of sensitive and stable SERS substrates or probes. This Minireview highlights recent progress in exploring metal nanoparticle-based substrates, especially gold nanoparticle-based substrates, for the detection of biomarkers released from bacterial spores. One recent example involves assemblies of gold nanoparticles on a gold substrate for the highly sensitive detection of dipicolinic acid (DPA), a biomarker for bacterial spores such as Bacillus anthracis. This type of substrate exploits a strong SERS effect produced by the particle-particle and particle-substrate plasmonic coupling. It is capable of accurate speciation of the biomarker but also selective detection under various reactive or non-reactive conditions. In the case of detecting Bacillus subtilis spores, the limit of detection is quite comparable (0.1 ppb for DPA, and 1.5 × 10(9) spores per L (or 2.5 × 10(-14) M)) with those obtained using silver nanoparticle-based substrates. Implications of the recent findings for improving the gold nanoparticle-based SERS substrates with ultrahigh sensitivity for the detection of bacterial spores are also discussed.

A reversible chemosensor for nitrite based on the fluorescence quenching of a carbazole derivative.

The carbazole derivative, with an amino group in 9-position (9-methylacryloylamino carbazole (MAC), has been utilized to prepare a fluorescent sensor and used for the determination of NO(2)(-) based on the reaction between nitrite (NO(2)(-)) and excess I(-) to form I(3)(-), which can quench the fluorescence of carbazole derivative. MAC, as a fluorescent carrier, has a terminal double bond and is covalently immobilized on a quartz glass plate surface by photo-polymerization to prevent the leakage of the dye. The sensor shows sufficient repeatability, selectivity, operational lifetime of 8 weeks, and a fast response of less then 30s. NO(2)(-) can be determined in the range between 1.0x10(-6) and 1.0x10(-4)moll(-1) with a detection limit of 8.0x10(-7)moll(-1) at pH of 2.0. The quenching mechanism is discussed. Most commonly coexisting ions do not interfer with the NO(2)(-) assay.

Molecularly imprinted TiO2 thin film using stable ground-state complex as template as applied to selective electrochemical determination of mercury

Molecular recognition sites for mercury ions were imprinted in TiO(2) film using stable ground-state complex of 1-amino-8-naphtol-3,6-disodium sulfonate (ANDS) and mercury ions as template. The complex ratio between mercury ions and ANDS was estimated to be 2:1. Compared with the controlled and pure TiO(2) electrodes, the imprinted electrode revealed selectivity towards the imprinted ions. Linear calibration plots for mercury ions were obtained and the regression equation was I(p) (muA)=4.29x10(-7)+19.40 [Hg(2+)] with a detection limit of 3.06x10(-9)mol/l. The imprinted electrode could be used for more than 1 month. Recoveries were calculated at both high and low concentrations, with a mean recovery of 99.6%.

Silver deposited polystyrene (PS) microspheres for surface-enhanced Raman spectroscopic-encoding and rapid label-free detection of melamine in milk powder

Silver nanoparticles coated amino modified polystyrene microspheres (PS-NH2/Ag NPs) with extremely high surface enhanced Raman scattering (SERS) activity and uniform surface morphology were created by precise controlling of deposition time. Nanojets that were formed underneath the individual microspheres could be used for nondestructive analysis of species adsorbed on the smooth gold or glass surface. A 10 fold enhancement of SERS was observed between PS-NH2/Ag NPs and gold surface compared to glass surface due to more effective coupling of surface plasmonic resonance. These microsphere SERS substrates could detect 2-Mercaptopyridine down to 10(-9)M. Four different thiol compounds have been successfully utilized as tags to prepare SERS encoded PS-NH2/Ag NPs microspheres. Furthermore, the potential application of these SERS substrate for rapid detection of melamine in milk powder was explored. A linear relationship was observed between SERS intensity and logarithm of melamine concentrations with the limit of detection (LOD) of 1.9 × 10(-8)mol/L. The promising advantages of easy sample pretreatment, low protein background interference, short detection time and low cost makes the PS-NH2/Ag NPs substrate a potential detection tool in the field of food safety.

Liposome-mediated enhancement of the sensitivity in immunoassay based on surface-enhanced Raman scattering at gold nanosphere array substrate.

A novel immunoassay based on surface-enhanced Raman scattering (SERS) has been developed. The method exploits the SERS-derived signal from reporter molecules (crystal violet, CV) encapsulated in antibody-modified liposome particles. The antigen is firstly captured by the primary antibody immobilized in microwell plates and then sandwiched by secondary antibody-modified liposome. The CV molecules are released from the liposome and transferred to specially designed substrate of gold nanosphere arrays with sub-10-nm gaps. The concentration of the antigen is indirectly read out by the SERS intensity of the CVs. The substrate used could substantially improve the sensitivity and reproducibility of SERS measurement. The SERS intensity responses are linearly correlated to logarithm of antigen concentration in the range of 1.0 x 10(-8) to 1.0 x 10(-4) gm L(-1) with a detection limit of 8 ng mL(-1). To our knowledge, this is the first report describing liposome-mediated enhancement of the sensitivity in immunoassay based on surface-enhanced Raman scattering. Experimental results show that the proposed method illustrates a potential prospect of applications in immunoassay.