A highly sensitive biosensor for detecting HPV 16 DNA was prepared based on Keggin-type polyoxometalate (SiW12)-grafted CdS quantum dots (SiW12@CdS QDs) and colloidal gold nanoparticles (Au NPs), which exhibited remarkable selectivity and sensitivity upon target DNA detection because of its excellent photoelectrochemical (PEC) response. Here, an enhanced photoelectronic response ability was achieved with the strong association of SiW12@CdS QDs by polyoxometalate modification, which was developed through a convenient hydrothermal process. Furthermore, on Au NP-modified indium tin oxide slides, a multiple-site tripodal DNA walker sensing platform coupled with T7 exonuclease was successfully fabricated with SiW12@CdS QDs/NP DNA as a probe for detecting HPV 16 DNA. Due to the remarkable conductivity of Au NPs, the photosensitivity of the as-prepared biosensor was improved in an I3−/I− solution and avoided the use of other regents toxic to living organisms. Finally, under optimized conditions, the as-prepared biosensor protocol demonstrated wide linear ranges (15–130 nM), with a limit of detection of 0.8 nM and high selectivity, stability, and reproducibility. Moreover, the proposed PEC biosensor platform offers a reliable pathway for detecting other biological molecules with nano-functional materials.
Herein, we report a “on-off” signal-switchable electrochemiluminescence (ECL) biosensor for simple, sensitive and quantitative detection of two kinds of virus genes, human immunodeficiency virus (HIV) and human papilloma virus (HPV-16) DNAs, by the integration of spherical nucleic acid (SNA) with CRISPR/Cas12a. The concept behind this approach is “on” signal based on a sandwich type assay after ECL luminophores of carbon dots (CDs) labeled SNA incubated with the biosensor in the presence of HIV DNA; and “off” signal upon the biosensor incubation with assistant DNA (HIV DNA sequence), CDs-labeled SNA and Cas12a/crRNA/HPV-16 DNA ternary complex relying on the collaterally cleavage of Cas12a. The cross-interference between HIV and HPV-16 DNAs can be avoided by adding Cas12a effector to the system or not. Using this strategy, HIV and HPV-16 DNAs are successfully quantitatively detection with detection limits of 30 fM and 0.32 pM (S/N = 3), respectively. Importantly, this system does not rely on multiplex signal reporting molecules, thus simplifying the detection system and avoiding the likelihood of cross interferences presented in the assay. Furthermore, multiplex detection of HIV/HPV-16 DNAs in human serum samples are successfully achieved within 2 h without additional nucleic acid amplification step. As demonstrated, the proposed biosensor has the potential for multiplex detection in clinical diagnosis.
The discrepancy of the electrostatic interaction of negatively charged signal molecules to long and short DNA strands of the modified electrode surface has been used for the first time to the develop an electrochemiluminescence (ECL) biosensor for human papillomavirus 16 (HPV 16) DNA detection. The short single-stranded capture probe (CP) was modified first on the surface of the gold electrode, which only has a small amount of negative charge. The electrostatic interaction between the negatively charged tris(2,2′-bipyridyl) ruthenium(II) chloride hexahydrate-doped SiO2 nanoparticles (Ru@SiO2 NPs) and CP is weak, hence Ru@SiO2 NPs easily diffuse to the surface of the electrode to generate a strong ECL signal. Hybrid chain reaction (HCR) amplification products (long strand dsDNA) were prepared in homogeneous solution in advance. When the target was present, the dsDNA can be connected on the electrode surface and cause the enhancement of the negative charge on the electrode surface. Owing to electrostatic interaction and steric hindrance, Ru@SiO2 NPs are difficult to diffuse to the electrode surface, resulting in a significantly reduced ECL signal. The decrease of ECL signal is linearly correlated with the logarithm of the HPV concentration under optimal conditions, with the detection range being 0.1 fM −5 pM with a limit of 1.41 aM. This innovative methodology expands the application of electrostatic interaction in ECL sensing, but can also easily develop biosensors for detecting other targets by changing the DNA sequence used in this strategy.
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