A synthetic DNA machine performs quasi-mechanical movements in response to external intervention, suggesting the promise of constructing sensitive and specific biosensors. Herein, a smart DNA walker biosensor for label-free detection of carcinoembryonic antigen (CEA) is developed for the first time by a novel cascade amplification strategy of exonuclease (Exo) III-assisted target recycling amplification (ERA) and DNA walker. ERA as the first stage of amplification generates the walker DNA, while the autonomous traveling of the walker DNA on the substrate-modified silica microspheres as the second stage of amplification produces an ultrasensitive fluorescent signal with the help of N-methylmesoporphyrin IX (NMM). The DNA machine as a biosensor could be applied for transducing and quantifying signals from isothermal molecular amplifications, avoiding the complicated reporter elements and thermal cycling. The present biosensor achieves a detection limit of 1.2 pg·mL within a linear range of 10 pg·mL to 100 ng·mL for CEA, along with a favorable specificity. The practical applicability of the biosensor is demonstrated by the detection of CEA in human serum with satisfactory results; thus, it shows great potential in clinical diagnosis.

The outbreak of rabies virus (RABV) in Asia and Africa has attracted widespread concern due to its 100% mortality rate, and RABV detection is crucial to its diagnosis and treatment. Herein, we report a sensitive and reliable strategy for the dualmodal RABV detection using pomegranate-shaped dendritic silica nanospheres fabricated with densely incorporated quantum dots (QDs) and horseradish peroxidase (HRP)-labeled antibody. The immunoassay involves the specific interaction between virus and nanospheres-conjugated antibody coupled with robust fluorescence signal originating from QDs and naked-eye discernible colorimetric signal on the oxTMB. The ultrahigh loading capacity of QDs enables the detection limit down to 8 pg/mL via fluorescence modality, a 348-fold improvement as compared with conventional enzyme-linked immunosorbent assay (ELISA). In addition, the detection range was from 1.20 × 10 2 to 2.34 × 10 4 pg/mL by plotting the absorbance at 652 nm with RABV concentrations with a detection limit of 91 pg/mL, which is nearly 2 order of magnitude lower than that of the conventional ELISA. Validated with 12 brain tissue samples, our immunoassay results are completely consistent with polymerase chain reaction (PCR) results. Compared with the PCR assay, our approach requires no complex sample pretreatments or expensive instruments. This is the first report on RABV diagnosis using nanomaterials for colorimetry-based prescreening and fluorescence-based quantitative detection, which may pave the way for virus-related disease diagnosis and clinical analysis.

A voltammetric sensor for Sunset Yellow was fabricated by polymerizing L-cysteine on the surface of a glassy carbon electrode. The modified electrode was characterized by cyclic voltammetry and electrochemical impedance spectroscopy. The electrochemical behavior and kinetic parameters of Sunset Yellow in phosphate buffer solution (pH 6.6) were investigated by cyclic voltammetry and chronocoulometry using the proposed sensor, and results showed that the electrochemical response of Sunset Yellow was significantly improved. The peak current (differential pulse voltammetry) of Sunset Yellow linearly increased with the concentrations in the range of 8.0 Â 10 À9 -7.0 Â 10 À7 mol L À1 , and the minimum detectable concentration of Sunset Yellow was estimated to be 4.0 Â 10 À9 mol L À1 .Moreover, the linear relationship between the peak current and the concentration of Sunset Yellow in the presence of Lemon Yellow was 1.0 Â 10 À8 -5.0 Â 10 À7 mol L À1 , with a minimum detectable concentration of 6.0 Â 10 À9 mol L À1 . The reported electrochemical sensor was excellent for the determination of Sunset Yellow because of merits such as extreme simplicity, low cost, high sensitivity, good stability and reproducibility.

No abstract

No abstract