Zhanfang Ma

L-cysteine functionalized gold nanoparticles for the colorimetric detection of Hg2+ induced by ultraviolet light

A simple, cost-effective yet rapid and sensitive colorimetric sensor for the detection of Hg(2+) using L-cysteine functionalized gold nanoparticles induced by ultraviolet radiation was developed. The sensitivity and selectivity of detection was also investigated. The L-cysteine modified gold nanoparticles can be induced to aggregate quickly in the presence of Hg(2+), especially with the assistance of ultraviolet radiation. The presence of Hg(2+) can be monitored by the colorimetric response of gold nanoparticles. The detection of Hg(2+) could be realized, after measuring the UV-vis spectra, with a detection limit of 100 nM. The selectivity of this method has been investigated by other divalent metal ions. The effective colorimetric sensor can be used for on-site and real-time Hg(2+) detection.

Optical DNA detection based on gold nanorods aggregation.

Sequence-specific DNA detection is important in various biomedical applications such as gene expression profiling, disease diagnosis and treatment, drug discovery and forensic analysis. Herein, the localized surface plasmon resonance properties of unmodified gold nanorods (GNRs) in 1 mM cetyltrimethyl-ammonium bromide solution were used for sensing DNA sequences, with good simplicity and sensitivity. The intensity of typical plasmon resonance absorption bands of the GNRs decreased with increasing cDNA concentration. The detection of a 30-mer single-stranded oligonucleotide as a model reached a detection limit of about 0.1 pM. This study will be significant for as-prepared GNRs for future application in biological systems.

Controllable colours and shapes of silver nanostructures based on pH: application to surface-enhanced Raman scattering

This paper reports for the first time that the shape of silver nanostructures on quartz slides, from a nanoprism to a nanodisc, can be easily realized within a few minutes simply by adjusting the pH value of the immersion solution. Different colours of the quartz slide covered with Ag nanostructures appeared, from deep blue to yellow, corresponding to the shapes of Ag nanostructures changing from nanoprisms to nanodiscs. Surface-enhanced Raman scattering (SERS) activities of the silver nanoprisms and nanodiscs (obtained through adjusting the pH values) were checked using p-aminothiophenol (p-ATP) as a probe molecule at both near-infrared (1064 nm) and visible light (514.5 nm) excitation. The results obtained further confirmed the enhancement mechanism of SERS based on the coupling between the surface plasmon resonance (SPR) of the substrates and the laser excitation wavelength. This work will be of great significance in understanding the SERS enhancement mechanism and in the fabrication of nanoparticle films for biosensing.

Electrochemical immunosensor based on nanoporpus gold loading thionine for carcinoembryonic antigen

Nanoporous gold (NPG) has recently received considerable attention in analytical electrochemistry because of its good conductivity and large specific surface area. A facile layer-by-layer assembly technique fabricated NPG was used to construct an electrochemical immunosensor for carcinoembryonic antigen (CEA). NPG was fabricated on glassy carbon (GC) electrode by alternatively assembling gold nanoparticles (AuNPs) and silver nanoparticles (AgNPs) using 1,4-benzenedimethanethiol as a cross-linker, and then AgNPs were dissolved with HNO3. The thionine was absorbed into the NPG and then gold nanostructure was electrodeposited on the surface through the electrochemical reduction of gold chloride tetrahydrate (HAuCl4). The anti-CEA was directly adsorbed on gold nanostructure fixed on the GC electrode. The linear range of the immunosensor was from 10 pg mL(-1) to 100 ng mL(-1) with a detection limit of 3 pg mL(-1) (S/N=3). The proposed immunosensor has high sensitivity, wide linear range, low detection limit, and good selectivity. The present method could be widely applied to construct other immunosensors.

Prussian blue-gold nanoparticles-ionic liquid functionalized reduced graphene oxide nanocomposite as label for ultrasensitive electrochemical immunoassay of alpha-fetoprotein.

In this work, poly(diallyldimethylammonium chloride) (PDDA) protected Prussian blue/gold nanoparticles/ionic liquid functionalized reduced graphene oxide (IL-rGO-Au-PDDA-PB) nanocomposite was fabricated. The resulting nanocomposite exhibited high biocompatibility, conductivity and catalytic activity. To assess the performance of the nanocomposite, a sensitive sandwich-type immunosensor was constructed for detecting alpha-fetoprotein (AFP). Greatly enhanced sensitivity for this immunosensor was based on triple signal amplification strategies. Firstly, IL-rGO modified electrode was used as biosensor platform to capture a large amount of antibody due to its increased surface area, thus amplifying the detection response. Secondly, a large number of Au-PDDA-PB was conjugated on the surface of IL-rGO, which meant the enrichment of the signal and the more immobilization of label antibody. Finally, the catalytic reaction between H2O2 and the IL-rGO-Au-PDDA-PB nanocomposite further enhanced the signal response. The signals increased linearly with AFP concentrations in the range of 0.01-100 ng mL(-1). The detection limit for AFP was 4.6 pg mL(-1). The immunosensor showed high sensitivity, excellent selectivity and good stability. Moreover, the immunosensor was applied to the analysis of AFP in serum sample with satisfactory result.