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It remains a significant challenge to study the interactions between metal ions and porphyrin molecules at single ion level. Here, we constructed a nanopore-based sensing for label-free and real-time analysis of the interaction between Cu 2+ and 5,10,15,20-tetrakis(4-sulfonatophenyl)-porphyrin (TPPS). The results demonstrate that emerging electronic signatures of the Cu 2+ -TPPS complex that is completely different form the original free TPPS were observed in the α-hemolysin (α-HL) nanopore. Based on the distinctive electronic signal patterns between TPPS and Cu 2+ -TPPS complex, the unique nanopore sensor can achieve a highly sensitive detection of Cu 2+ in aqueous media. The frequency of signature events showed a linear response toward the concentration of Cu 2+ in the range of 0.03 µM – 1.0 μM, with a detection limit of 16 nM (S/N = 3). The sensing system also exhibited high selectivity against other metal ions, and the feasibility of this approach for practical applications was demonstrated with the determination of Cu 2+ in running water. [ABSTRACT FROM AUTHOR]

Circulating tumor DNA (ctDNA) in the blood is an important biomarker for noninvasive diagnosis, assessment, prediction and treatment of cancer. However, sensing performance of solid nanopore is limited by the fast kinetics of small DNA targets and unmatched dimensions. Here, we combines hybridization chain reaction (HCR) with nanopore detection to translate the presence of a small DNA target to characteristic nanopore signals of a long nicked DNA polymer. The amplification of nanopore signals obtained by HCR not only overcomes the functional limitation of solid nanopore, but also significantly elevates both selectivity and signal-to-noise ratio, which allows to detect ctDNA at a detection limit of 2.8 fM (S/N = 3) and the single-base resolution. Furthermore, the proposed method can apply in detection of ctDNA of KRAS G12DM in serum sample. • We have constructed HCR-nanopore sensing system and applied in the detection of ctDNA. • The sensing strategy exhibited well selective and the detection limit is 2.8 fM. • The proposed method can apply in detection of ctDNA in serum sample. • The method potentially offers a simple and non-invasive liquid biopsy for diagnosing cancer. [ABSTRACT FROM AUTHOR]

Nanopores as artificial biomimetic nanodevices are of great importance for their applications in biosensing, nanomedicine and bioelectronics. However, it remains a challenge to detect small biomolecules especially small-sized proteins with high sensitivity and selectivity. In the article, we report a simple and efficient method for small-sized protein detection by constructing biphasic-pulse nanopore biosensor. Unlike the traditional resistive pulse sensing, the biphasic-pulse event can provide unique and abundant fingerprint information. Although the nanopore biphasic-pulse electrical signal is originated from both the molecular exclusion electrical resistance and the surface-charged effect of confined molecule, its frequency and amplitude of the waveform can be adjusted by pH, applied potential and salt concentration. Based on the frequency of the biphasic pulse, nanomolar concentration of proteins could be specifically detected and the limit of detection is 1.2 nM. In addition, the biphasic-pulse nanopore shows well discrimination in similar-sized protein detection and its signal generation is highly reproducible. The nanopore biphasic-pulse biosensor should have broad applications as a new generation of powerful single-molecule device. • A label-free nanopore biphasic-pulse biosensor was constructed for selective detection of protein. • The biphasic-pulse waveshapes can be adjusted by pH, voltage and salt concentration. • The method shows high sensitivity and selectivity to lysozyme and the LOD is 1.2 nM. • This biosensor should have broad applications as a powerful single-molecule nanodevice. [ABSTRACT FROM AUTHOR]