We demonstrate herein a newly developed lable-free photoelectrochemical immunosensor using a CdS quantum dots (QDs) multilayer film coupled with a biospecific interaction. The CdS QDs multilayer film was prepared by layer-by-layer assembling positively charged poly(dimethyldiallylammonium chloride) (PDDA) and thioglycolic acid (TGA)-capped water-soluble CdS QDs with negative charges on the surface of an indium−tin oxide (ITO) electrode. Ascorbic acid (AA) was exploited as an efficient and nontoxic electron donor for scavenging photogenerated holes under mild solution medium. The photoexcitation of CdS QDs modified electrode potentiostated at 0 V (vs. Ag/AgCl) in the presence of 0.1 M AA led to a stable anodic photocurrent. To perform the immunoassay, goat antimouse IgG was conjugated onto CdS QDs modified electrode by using the classic EDC coupling reactions between COOH groups on the surfaces of the TGA capped CdS QDs and NH2 groups of the antibody. The concentrations of mouse IgG were measured through the decrease in photocurrent intensity resulting from the increase in steric hindrances due to the formation of the immunocomplex. The synthetic conditions (different Cd/S ratio and different pH) of CdS QDs and the number of PDDA/CdS bilayers could influence the photoelectrochemical properties of CdS QDs modified electrodes used for immunosensor construction. Under the optimal conditions, a linear relationship between photocurrent decrease and mouse IgG concentration was obtained in the range of 10 pg/mL to 100 ng/mL with a detection limit of 8.0 pg/mL. This strategy opens a new perspective for the application of QDs, which might be of great significance for QDs in photoelectrochemical bioanalysis in the future.
With DNA as a rigid spacer, Ag nanoparticles (NPs) were bridged to CdS quantum dots (QDs) for the stimulation of exciton-plasmon interactions (EPI) in a photoelectrochemical (PEC) system. Due to their natural absorption overlap, the exciton of the QDs and the plasmon of Ag NPs could be induced simultaneously. The EPI resonant nature enabled manipulating photoresponse of the QDs via tuning interparticle distances. Specifically, the photocurrent of the QDs could be greatly attenuated and even be completely damped by the generated EPI. The work opens a different horizon for EPI investigation through an engineered PEC nanosystem, and provides a viable mechanism for new DNA sensing protocol.
Herein we demonstrate the protocol of a biocatalytic precipitation (BCP)-based sandwich photoelectrochemical (PEC) horseradish peroxidase (HRP)-linked immunoassay on the basis of their synergy effect for the ultrasensitive detection of mouse IgG (antigen, Ag) as a model protein. The hybrid film consisting of oppositely charged polyelectrolytes and CdS quantum dots (QDs) is developed by the classic layer by layer (LbL) method and then employed as the photoactive antibody (Ab) immobilization matrix for the subsequent sandwich-type Ab-Ag affinity interactions. Improved sensitivity is achieved through using the bioconjugates of HRP-secondary antibodies (Ab(2)). In addition to the much enhanced steric hindrance compared with the original one, the presence of HRP would further stimulate the BCP onto the electrode surface for signal amplification, concomitant to a competitive nonproductive absorption that lowers the photocurrent intensity. As a result of the multisignal amplification in this HRP catalyzed BCP-based PEC immunoassay, it possesses excellent analytical performance. The antigen could be detected from 0.5 pg/mL to 5.0 ng/mL with a detection limit of 0.5 pg/mL.
Due to the undesired impact of gravity, experimental studies of energy-dissipative gaseous systems are difficult to carry out on ground. In the past several years, we developed a series of experimental devices suitable for various kinds of microgravity platforms. The central idea adopted in our devices is to use long-range magnetic forces to excite all the particles within the system. Through the development of our devices, different component configurations, excitation protocols, and image-capturing methods have been tried and optimized to achieve best excitation and the maximum capability for data analysis.
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