Yunlong Zeng

A novel label-free multi-throughput optical biosensor based on localized surface plasmon resonance

A novel and sensitive multi-throughput localized surface plasmon resonance (MLSPR) biosensor was developed for the first time. Various gold nanorods with different aspect ratios were used to fabricate the optical sensor. Five kinds of gold nanorods with different aspect ratios were chosen to construct five throughputs of MLSPR. Various LSPR peaks imply that different acceptor-ligand pairs can be detected simultaneously in the wavelength range from 530 to 940nm. The biosensor immobilized on glass slides was applied to label-free detection between acceptor and ligand. The MLSPR-based optical biosensor can be used to detect three antigen-antibody pairs simultaneously. The biosensor proposed herein is easy to fabricate, and its operation procedure is convenient as labeling procedure is unnecessary.

A novel method for iodate determination using cadmium sulfide quantum dots as fluorescence probes

We have developed a novel method for the determination of iodate based on the carboxymethyl cellulose-capped CdS quantum dots (QDs). Factors affecting the iodate detection were investigated, and the optimum conditions were determined. Under the optimum conditions, the relative fluorescence intensity of CdS quantum dots was linearly proportional to IO(3)(-) over a concentration range from 1.0 × 10(-8) to 1.0 × 10(-5) mol L(-1) with a correlation coefficient of 0.9987 and a detection limit of 6.0 nmol L(-1). Iodide, being oxidized by bromine to form iodate, was detected indirectly. The method was successfully applied to the determination of iodate and total amount of iodine in table salt samples. The related mechanism was also discussed.

Label-free optical biosensor based on localized surface plasmon resonance of immobilized gold nanorods

We describe the fabrication and characterization of a localized surface plasmon resonance (LSPR) biosensor that utilizes gold nanorods immobilized as the optical transducer which requires the intensity change at a single wavelength to be monitored as a function of receptor-analyte binding at the nanorod surface. In contrary to free gold nanorods suspended in an aqueous solution with high sensitivity to the longitudinal plasmon wavelength to the surrounding environment, the intensity of the longitudinal plasmon band based on immobilized gold nanorods is more sensitive to changes in the surrounding dielectric properties than the change in the longitudinal plasmon wavelength. Quantitative calculation gives a linear equation between the concentration (X) of the test sample and intensity of LPB (Y) as Y=0.0881+12.9502X and 0.1 pM anti-goat can be detected using this IgG probe in this study. This sensor chip made of immobilized gold nanorods is very stable. The immobilized gold nanorods preserved under 4 degrees C for 1 year yield almost the same extinction spectrum as the original nanorods. This study reveals a reliable and sensitive method to measure the intensity of longitudinal plasmon bands based on the highly stable LSPR substrate. Moreover, the performance is comparable to dynamic SPR measurements in immunoassays and can monitor the receptor-analyte reactions in real time.

Optical and biological sensing capabilities of Au2S/AuAgS coated gold nanorods.

Gold nanorods coated with a multiplex component, namely Au(2)S/AuAgS coated gold nanorods, are produced without precipitation and aggregation among the nanorods. Both the thickness of the shell and size of the core can be readily controlled by this technique allowing one to tune the plasmon resonance of the nanocomposites over a range of several hundred nanometers. These Au(2)S/AuAgS coated gold nanorods exhibit interesting optical properties and are suitable for many biological sensing applications. Functionalization of the Au(2)S/AuAgS coated gold nanorods is achieved by manipulating the affinity between the Au(2)S/AuAgS and thiol compounds. Biomolecules can be covalently attached via the NH(2) bond of the antibodies to the NHS-terminated nanorods. The longitudinal peaks of the Au(2)S/AuAgS coated gold nanorods are extremely sensitive to the refractive index changes induced by target binding, suggesting that they are excellent sensors for target-specific binding events and have the potential to achieve single-molecule sensitivity in microspectroscopy.

Multiplex plasmonic sensor for detection of different metal ions based on a single type of gold nanorod.

In this paper, a label-free multiplex plasmonic sensor has been developed to selectively determine different metal ions including Fe(3+), Hg(2+), Cu(2+), and Ag(+) ions based on a single type of gold nanorod (GNR). Under proper conditions, these metal ions can react with GNRs, resulting in changes of nanostructure and composition. The determination of Fe(3+), Hg(2+), Cu(2+), and Ag(+) ions is therefore readily implemented due to changes of longitudinal plasmon wavelength (LPW) of nanorods. Moreover, the GNR-based assay can not only determine all four kinds of metal ions successively but also can detect which of any one or several kinds of metal ions. This assay is sensitive to detect Fe(3+), Hg(2+), Cu(2+), and Ag(+) as low as 10(-6), 10(-8), 10(-10), and 10(-8) M, respectively. Importantly, the special nanostructure and composition of the nanorods are induced by these metal ions, which allow this sensor to maintain high selectivity to determine these metal ions. This nanosensor abrogates the need for complicated chemosensors or sophisticated equipment, providing a simple and highly selective detection platform.

Sensitive and simultaneous detection of different disease markers using multiplexed gold nanorods

A multiplexed bioanalytical assay is produced by incorporating two types of gold nanorods (GNRs). Besides retaining the desirable features of common GNRs LSPR sensors, this sensor is easy to fabricate and requires only a visible-NIR spectrometer for detection. This assay can simultaneously detect different acceptor-ligand pairs by choosing the proper GNRs possessing various LPWs in a wide detection wavelength range and can be developed into a high-throughput detection method. This bioanalytical assay allows easy detection of human serum specimens infected by S. japonicum and tuberculosis (TB) from human serum specimens (human serum/Tris-HCl buffer ratio=1:10(4)) without the need for sample pretreatment. The technique is very sensitive compared to other standard methods such as indirect hemagglutination assays (IHA) that require a serum concentration ratio of larger than 1:20 and enzyme-linked immunosorbent assays (ELISA) requiring a ratio larger than 1:100. This methodology can be readily extended to other immunoassays to realize wider diagnostic applications.

High-sensitivity biosensors fabricated by tailoring the localized surface plasmon resonance property of core-shell gold nanorods

An enhanced sensitive biosensor has been developed to detect biological targets by tailoring the localized surface plasmon resonance property of core-shell gold nanorods. In this new concept, a shell layer is produced on gold nanorods by generating a layer of chalcogenide on the gold nanorod surface after attachment of the recognition reagent, namely, goat IgG and antigen of schistosomiasis japonica. The bioactivity of these attached biomolecules is retained and the sensitivity of this biosensor is thus enhanced significantly. The plasmonic properties of the gold nanorods attached with the biomolecules can be adjusted and the plasmon resonance wavelength can be red-shifted up to several hundred nanometers in the visible or near infrared (NIR) region, which is extremely important to biosensing applications. This leads to a lager red-shift in the localized surface plasmon resonance absorption compared to the original gold nanorod-based sensor and hence offers greatly enhanced sensitivity in the detection of schistosomiasis japonica. The human serum infected with schistosomiasis japonica diluted to 1:50,000 (volume ratio, serum/buffer solution) can be detected readily. The technique offers enhanced sensitivity and can be easily extended to other sensing applications based on not only immuno-recognition but also other types of specific reactions.

Enhanced fluorescence of chitosan based on size change of micelles and application to directly selective detecting Fe3+ in humanserum

In this paper, we have developed an approach to significantly enhance fluorescence of chitosan by simply heated the inherently low fluorescent chitosan aqueous solution. Enhanced blue fluorescence of chitosan solution was observed as originated from the formation of small size of chitosan micelle after long time heated. The fluorescence of chitosan micelles was quenched and recovered when Fe³⁺ ions were combined and released from chitosan micelles. Therefore, chitosan without modification of functional groups can recognize Fe³⁺ with very high selectivity. As a result, a new fluorescence sensor for sensitively detecting Fe³⁺ ion based on the change of chitosan micelles sizes was subsequently fabricated. This enhanced fluorescence enables the chitosan sensor to be sensitive to low concentrations of Fe³⁺, and it is linear responsive in the range of 1.96×10⁻⁸ to 2.00×10⁻⁵ M. Importantly, this novel sensor may be applied in human serum for direct detection of Fe³⁺ ion without sample pretreatment. Analysis of 5 samples of human serum shows that the average concentration of Fe³⁺ is 26.95 μM, which is consistent with the results determined by other methods. Moreover, the advantage of chitosan-based assay is that Fe³⁺ rather than Fe²⁺ in human serum can be directly measured, avoiding costly, time-consuming and complex process.

Ultrasensitive Determination of Copper in Complex Biological Media Based on Modulation of Plasmonic Properties of Gold Nanorods

Accurate determination of copper in complex biological media such as cells is quite difficult, and an analytical strategy based on copper-modulated formation of core-shell gold nanorods is described. Selective and label-free sensing can be achieved by measuring the change in the localized surface plasmon resonance absorption. The technique can determine trace amounts of copper in human serum, urine, and red blood cells without or with minimal sample pretreatment. The Cu detection limits are 20.67 μM in human serum, 0.193 μM in human urine, and 3.09 × 10(-16) g in a single cell. The advantages of the technique are the high selectivity, simple or no sample pretreatment, and label free. Boasting a practical detection limit down to 2 fM, only 10(3) red blood cells are needed to conduct the analysis and the technique may be extended to the detection of trace amounts of copper in a single cell.

Label-free optical biosensors based on Au2S-coated gold nanorods

In this research, two new types of optical biosensors were explored from Au(2)S-coated gold nanorods (Au(2)S-coated GNRs) chemically attached with human IgG as recognizing probes. The first type of biosensors were suspended GNRs and exhibited sensitive shift of longitudinal plasmon wavelength in response to anti-human IgG, with the limit of detection down to 67 pM. The second type of sensors were on-chip-immobilized GNRs, able to be used repeatedly through measuring the change of plasmon absorption intensity at a fixed wavelength, with the limit of detection down to 33 pM. The latter sensors suited for dynamic measurements, having linear response over rang from 33 pM to 1.35 nM. Both the types of sensors not only preserved the desirable features of common GNR sensors but also easy for preparation and manipulation. The concept and methodology suggested in this study can serve as the basis to develop new methods for molecular binding events or other applications like in medical researches.