A photoelectrochemical biosensor based on ZnIn2S4@AuNPs coupled with circular bipedal DNA walker for signal-on detection of circulating tumor DNA

Ingenious dual-circle DNA walker-mediated electrochemical biosensor for rapid and ultrasensitive detection of microRNA

In this work, an ingenious dual-circle DNA walker (DCDW) with pretty fast walking speed and high amplification efficiency was developed for rapid and ultrasensitive electrochemical detection of microRNA-221 (miRNA-221) related to liver cancer, combined with the toehold-mediated strand-displacement reactions (TSDRs). Impressively, compared with the traditional DNA walker, the DCDW with unique double-stranded interlocked DNA nanostructure not only possesses higher stability, flexibility, and anti-entanglement ability, but also enables more functional domain in a smaller area, thereby enhancing the local concentration, which can greatly improve the working efficiency. As a validation, the electrochemical biosensor realized rapid and ultrasensitive detection of miRNA-221 with a reaction time of 15 min and detection limit down to 1.9 aM, and had been applied in MHCC97L and HeLa cancer cell lysates, thus providing an innovative insight to design intelligent functional interlocked DNA walkers for ultimate application in the construction of biosensing platform and miRNA detection in biological sample.

A "signal-off" anodic photoelectrochemical sensor based on ZnIn2S4/TiO2 heterojunction for dopamine detection

Dopamine (DA) is an important neurotransmitter. Abnormal levels of it in human body can increase the risk of many neurological diseases. Thus, developing a simple, sensitive detection method of DA is crucial. In this paper, we reported a "signal-off" anodic PEC sensor based on fluorine-doped tin oxide (FTO) glass modified ZnIn2S4/TiO2 heterojunction (ZnIn2S4/TiO2/FTO) for DA detection. The experimental results show that the ZnIn2S4/TiO2/FTO electrode prepared by two-step hydrothermal method has a good photocurrent response performance under visible light. After incubation with DA, the photocurrent response decreases significantly because DA can rapidly oxidizes to polydopamine (PDA) through the action of superoxide radical (·O2-) and hydroxyl radical (·OH) intermediate species, which are intermediates produced by the ZnIn2S4/TiO2/FTO electrode under visible light irradiation. The constructed PEC sensor has a good linear relationship in the concentration range from 0.5 to 1000.0 μM, and its detection limit is 0.253 μM. In addition, the results of the proposed PEC sensor in real serum samples are satisfactory. The PEC sensor provides a promising platform for DA detection, laying the foundation for future advances in disease diagnosis and prevention.

Triple quenching effect of nanozyme catalyzed precipitation combined with enzyme-free amplification for photoelectrochemical biosensing of circulating tumor DNA

In this work, a new photoelectrochemical (PEC) biosensor based on triple quenching effect of nanozyme catalyzed precipitation to PEC signal of MgIn2S4 was constructed for ultrasensitive detection of circulating tumor DNA (ctDNA). Enzyme-free amplification technology was used to convert target ctDNA into a large number of product chains (PC) to improve the detection sensitivity. Co3O4 nanozyme with excellent peroxidase (POD)-like activity was introduced to the surface of MgIn2S4 by PC. Co3O4 could oxidize chromogenic agent 3-Amino-9-ethylcarbazole (AEC) to produce red insoluble precipitation in the presence of H2O2, resulting in the PEC signal "off" of MgIn2S4 to achieve ultrasensitive detection of ctDNA. In particular, Co3O4 nanozyme showed three synergistic quenching effects on PEC signal of MgIn2S4, which contributed greatly to improving the detection sensitivity. Firstly, the light absorption range of Co3O4 could reach 1000 nm, and compete with MgIn2S4 for light absorption. Secondly, the produced red precipitation belonged to the insulating material and had large electrochemical impedance, which hindered the transmission of photogenerated carriers. Thirdly, the precipitation also prevented the electron donor ascorbic acid (AA) from transferring electrons to MgIn2S4. This biosensor provided a promising sensitive PEC detection technology for ctDNA, and further broadened the application of nanozymes in the field of PEC analysis.

AgI Precipitation Induced Polarity Reversal with Formation of Z-Type Heterojunction for Photoelectrochemical Sensing

Regulating photocurrent polarity is highly attractive for fabricating photoelectrochemical (PEC) biosensors with improved sensitivity and accuracy in practical samples. Here, a new approach that adopts the in situ generated AgI precipitate and AgNCs to reversal Bi2WO6 polarity with formation of Z-type heterojunction was proposed for the first time, which coupled with a high-efficient target conversion strategy of exonuclease III (Exo III)-assisted triple recycling amplification for sensing miRNA-21. The target-related DNA nanospheres in situ generated on electrode with loading of plentiful AgI and AgNCs not only endowed the photocurrent of Bi2WO6 switching from the anodic to cathodic one due to the changes in the electron transfer pathway but also formed AgI/AgNCs/Au/Bi2WO6 Z-type heterojunction to improve the photoelectric conversion efficiency for acquiring extremely enhanced PEC signal, thereby significantly avoiding the problem of high background signal derived from traditional unidirectional increasing/decreasing response and false-positive/false-negative. Experimental data showed that the PEC biosensor had a low detection limit down to 0.085 fM, providing a new polarity-reversal mechanism and expected application in diverse fields, including biomedical research and clinical diagnosis.

Self-signal electrochemical identification of circulating tumor DNA employing poly-xanthurenic acid assembled on black phosphorus nanosheets

A self-signal electrochemical identification interface was prepared for the determination of circulating tumor DNA (ctDNA) in peripheral blood based on poly-xanthurenic acid (PXTA) assembled on black phosphorus nanosheets (BPNSs) acquired through simple ultrasonication method. The BPNSs with large surface area could be integrated with the xanthurenic acid (XTA) monomers by right of physisorption, and hence improved the electropolymerization efficiency and was beneficial to the enlargement of the signal response of PXTA. The assembled PXTA/BPNSs composite with attractive electrochemical activity was adopted as a platform for the recognition of DNA immobilization and hybridization. The probe ssDNA was covalently fixed onto the PXTA/BPNSs composite with plentiful carboxyl groups through the terminate free amines of DNA probes by use of the 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide and N-hydrosulfosuccinimide cross-linking reaction, accompanied with the decline of the self-signal response. When the hybridization between the probe ssDNA and the target DNA was accomplished, the self-signal response of the composite interface reproduced by virtue of the shaping of helix construction. The determination limit of the assembled DNA identification interface was 2.1 × 10-19 mol/L, and the complementary target DNA concentrations varied from 1.0 × 10-18 mol/L to 1.0 × 10-12 mol/L. The DNA identification platform displayed magnificent sensitivity, specificity and stability, and was efficaciously implemented to the mensuration of ctDNA derived from colorectal cancer.

Recent advances in the applications of DNA frameworks in liquid biopsy: A review

Cancer is one of the serious threats to public life and health. Early diagnosis, real-time monitoring, and individualized treatment are the keys to improve the survival rate and prolong the survival time of cancer patients. Liquid biopsy is a potential technique for cancer early diagnosis due to its non-invasive and continuous monitoring properties. However, most current liquid biopsy techniques lack the ability to detect cancers at the early stage. Therefore, effective detection of a variety of cancers is expected through the combination of various techniques. Recently, DNA frameworks with tailorable functionality and precise addressability have attracted wide spread attention in biomedical applications, especially in detecting cancer biomarkers such as circulating tumor cells (CTCs), exosomes and circulating tumor nucleic acid (ctNA). Encouragingly, DNA frameworks perform outstanding in detecting these cancer markers, but also face some challenges and opportunities. In this review, we first briefly introduced the development of DNA frameworks and its typical structural characteristics and advantages. Then, we mainly focus on the recent progress of DNA frameworks in detecting commonly used cancer markers in liquid-biopsy. We summarize the advantages and applications of DNA frameworks for detecting CTCs, exosomes and ctNA. Furthermore, we provide an outlook on the possible opportunities and challenges for exploiting the structural advantages of DNA frameworks in the field of cancer diagnosis. Finally, we envision the marriage of DNA frameworks with other emerging materials and technologies to develop the next generation of disease diagnostic biosensors.

A new strategy based on a cascade amplification strategy biosensor for on-site eDNA detection and outbreak warning of crown-of-thorns starfish

Population outbreaks of the crown-of-thorns starfish (COTS) seriously threaten the sustainability of coral reef ecosystems. However, traditional ecological monitoring techniques cannot provide early warning before the outbreaks, thus preventing timely intervention. Therefore, there is an urgent need for a more accurate and faster technology to predict the outbreaks of COTS. In this work, we developed an electrochemical biosensor based on a programmed catalytic hairpin assembly (CHA) and hybridization chain reaction (HCR) cyclic amplification strategy for sensitive and selective detection of COTS environmental DNA (eDNA) in water bodies. This biosensor exhibited excellent electrochemical characteristics, including a low limit of detection (LOD = 18.4 fM), low limit of quantification (LOQ = 41.1 fM), and wide linear range (50 fM - 10 nM). The biosensing technology successfully allowed the detection of COTS eDNA in the aquarium environment, and the results also demonstrated a significant correlation between eDNA concentration and COTS number (r = 0.990; P < 0.001). The reliability and accuracy of the biosensor results have been further validated through comparison with digital droplet PCR (ddPCR). Moreover, the applicability and accuracy of the biosensor were reconfirmed in field tests at the COTS outbreak site in the South China Sea, which has shown potential application in dynamically monitoring the larvae before the COTS outbreak. Therefore, this efficient electrochemical biosensing technology offers a new solution for on-site monitoring and early warning of the COTS outbreak.

A signal-on photoelectrochemical aptasensor based on ferrocene labeled triple helix DNA molecular switch for detection of antibiotic amoxicillin

A sensitive signal-on photoelectrochemical aptasensor for antibiotic determination was constructed based on the energy level matching between ferrocene and CuInS2. P-type CuInS2 microflower was complexed with reduced graphene oxide (CuInS2/rGO) to get photocathode current with good photoelectric conversion efficiency and stability. Then, hairpin DNA (HP) was covalently bonded to the electrode surface. A triple helix DNA (THMS) was used as a molecular switch. After the specific recognition between target and THMS in homogeneous solution, ferrocene labeled probe (Fc-T2) was released. Finally, Fc-T2 was captured by the HP, which leaded the obvious increase of photocurrent for the energy level matching between ferrocene and CuInS2. The increase of the photocurrent signal was proportional to the concentration of target amoxicillin (AMOX), the linear range was 100 fM-100 nM with detection limit of 19.57 fM. Meanwhile, the method has been successfully applied for milk and lake water samples analysis with satisfactory results.

Rapid detection of melamine by DNA Walker mediated SERS sensing technique based on signal amplification function

A new method is proposed for detecting typical melamine dopants in food using surface-enhanced Raman scattering (SERS) biosensing technology. Melamine specific aptamer was used as the identification probe, and gold magnets (AuNPs@MNPs) and small gold nanoparticles (AuNPs@MBA) were used as the basis for Raman detection. The Raman signal of the detection system can directly detect melamine quantitatively. Under optimized conditions, the detection of melamine was carried out in the low concentration range of 0.001-500 mg/kg, the enhancement factor (EF) was 2.3 × 107, and the detection limit was 0.001 mg/kg. The method is sensitive and rapid, and can be used for the rapid detection of melamine in the field environment.

Exonuclease-catalyzed recycling and annular four-footed DNA walking amplification-assisted "on-off-super on" signal transitions for photoelectrochemical biosensing of kanamycin

Photoelectrochemical (PEC) biosensors have exhibited a promising potential for assays of a large variety of analytes; however, how to realize their low background-based "super on" signal output is still a great challenge. Herein, we report a novel multiple nucleic acid amplification-assisted "on-off-super on" signal transition mechanism for the PEC biosensing of kanamycin antibiotics. The biosensing platform was constructed on a perylene-3,4,9,10-tetracarboxylic dianhydride-based photoelectrode, and its strong photocurrent could be well inhibited by an anchored ferrocene (Fc)-labeled hairpin DNA to produce a low background signal. Two target biorecognition-triggered exonuclease III-catalytic reactions were adopted to produce an annular four-footed DNA walker (AFW) and a methylene blue (MB)-labeled DNA strand. By using their synergistic effect to release Fc quenchers and simultaneously capture MB sensitizers, a "super on" signal output was realized. As a result, a very wide linear range from 10 fg mL-1 to 10 ng mL-1 and an ultra-low detection limit of 7.8 fg mL-1 were obtained. Meanwhile, the aptamer recognition-based homogeneous reaction and AFW-based multiple nucleic acid amplification effectively simplified the assay manipulation and well ensured the repeatability of the method. The satisfactory sample experiment results indicated its good reliability and accuracy for the antibiotic residue analysis application.