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  • Always some extra effort may make great progress

    2022-08-18

    Always, some extra effort may make great progress in sensing platform, for example, Ma's group discovered luminescent iridium (Ⅲ) complexes which were highly selective for G-quadruplex DNA and Al3+, then they utilized these complexes to develop a series of G-quadruplex-based probes and chemosensor respectively for the detection of disease-related targets [[22], [23], [24], [25]]. Some other transition-metal complexes with special properties were subsequently exploited [26,27], combining with appropriate techniques or strategies, high-performance sensing platform were fabricated for potential therapeutic assessment. For purpose of improving detection sensitivity, a series of signal amplification strategies have been applied in the construction of DNA sensing platform. Among them, bio-barcode amplification (BCA) strategy in sandwich DNA sensing has emerged as an effective way [[28], [29], [30]]. This strategy using oligonucleotide modified gold nanoparticles (AuNPs) to hybridize target DNA, then target DNA can concatenate magnetic beads through a biotin modified DNA probe, sandwiching the targets to accomplish detection. However, the conventional BCA-based assay needs to release the barcode DNA strands and immobilize it on a microarray, which may lead to cross hybridization and increase the experimental complexity [31,32]. Recently, a new kind of BCA-based assay, termed DNA-functionalized gold nanoparticles (DNA-AuNPs), was exploited to achieve the sensitivity of polymerase chain reaction (PCR) without enzymes [33,34]. The DNA-AuNPs conjugate was prepared by AuNPs and two-component ssDNA, one of the ssDNA components is used to recognize the target, while the other serves as bar-code DNA strands to generate signals that reducing the cross-reaction of targets with DNA loaded on the same AuNP [35,36]. Furthermore, hybridization chain reaction (HCR) is an isothermal nucleic L-Phenylephrine amplification strategy, which has also been shown to be as sensitive as PCR [[37], [38], [39]]. The conception of HCR was first introduced for the detection of DNA in 2004 [40]. Two kinds of different DNA hairpin probes which contain complementary fragments each other can maintain stable forms in the hybridization solution. Nevertheless, when initiator DNA strands are added, a succession of hybridization events will be triggered because the two partially complementary DNA hairpin probes hybridize with each other to form DNA polymers with nicked double helices. Since each counterpart of the DNA initiators can touch off a HCR process, leading to combining a large amount of oligonucleotides, which supports enormous possibilities for signal amplification. Moreover, HCR is a unique assembly process which can work under common conditions without enzyme or special equipment. These salient properties make HCR an absorbing strategy in construction of sensing platform for detection of DNA [41,42], proteins [37], cells [43] and metal ions [44]. Herein, a label-free and highly sensitive ECL biosensing method for TDG activity detection was proposed based on signal amplification strategy of DNA-AuNPs triggered HCR with Ru(phen)32+ as ECL indicator. In this paper, AuNPs were functionalized with two kinds of different DNA sequences (denoted as ssDNA1 and ssDNA2) to form DNA-AuNPs structure. Sequences ssDNA1 in the structure can hybridize with hairpin probe DNA (hp-DNA) which was incubated with TDG and Endonuclease IV (EnIV) on the electrode surface, leading to capture of DNA-AuNPs onto the electrode. Whereas ssDNA2 can act as initiator strands to trigger HCR, the secondary amplification element, forming a nicked double helices DNA polymer. Consequently, numerous Ru(phen)32+ molecule, an ECL signal reporter, which can readily insert into the groove of nicked double helices DNA polymer to generate amplified ECL signal L-Phenylephrine [45,46]. Coupling DNA-AuNPs with HCR amplification strategy, we developed the ECL biosensing method which could be applied to detect the TDG activity with high sensitivity, reliability and robustness.