Ovarian cancer, known as \"silent killer\", is a gynocological cancer with high mortality that usually diagnosed in the late stages. Gold standard immunoassay technique is evaluation of CA-125 levels which is not merely specific to ovarian cancer. Therefore, there is a need for sensitive determination of more specific biomarkers. miR-200 family is RNA nucleic acids that known to be upregulated in the presence of ovarian cancer. Since diagnosis based on a single biomarker is prone to generate misleading results, it is important to develop point-of-care systems that allow diagnosis of multiple miRNAs. Herein, an electrochemical nanobiosensor platform was developed for the multiplexed and simultaneous detection of miR-200c and miR-141. Biorecognition part was constitutued of methylene blue and ferrocene labeled hairpin DNA probes immobilized onto carboxylated graphene oxide modified pencil graphite electrodes. Their hybridization with miRNAs were examined upon \"signal-off\" approach using Square Wave Voltammetry. The platform demonstrated a linear detection range of 0.1 pM to 10 nM for both miR-141 and miR-200c, with low detection limits of 0.029 pM and 0.026 pM, respectively. We assume that the developed biosensor platform may pave the way in early diagnosis of the disease and the development of more effective treatment strategies.

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.

Detecting dopamine (DA) in biological samples is vital to understand its crucial role in numerous physiological processes, such as motion, cognition, and reward stimulus. In this work, p-type graphene on sapphire, synthesized via chemical vapor deposition, serves as substrate for the preparation of p-type Cu2-xS films through solid-phase sulfurization. The optimized Cu2-xS/graphene heterostructure, prepared at 250 °C using a 15-nm copper film sulfurized for 2 h, exhibits superior electron transfer performance, ideal for electrochemical sensing. It is confirmed that the spontaneous charge transfer from graphene to Cu2-xS, higher Cu(II)/Cu(I) ratio (~ 0.8), and the presence of well-defined nanocrystalline structures with an average size of ~ 35 nm in Cu2-xS significantly contribute to the improved electron transfer of the heterostructure. The electrochemical sensor based on Cu2-xS/graphene heterostructure demonstrates remarkable sensitivity towards DA, with a detection limit as low as 100 fM and a dynamic range greater than 109 from 100 fM to 100 μM. Additionally, it exhibits excellent selectivity even in the presence of uric acid and ascorbic acid 100 times higher, alongside notable storage and measurement stability and repeatability. Impressively, the sensor also proves capable of detecting DA concentrations as low as 100 pM in rat serum, showcasing its potential for clinically relevant analytes and promising applications in sensitive, selective, reliable, and efficient point-of-care diagnostics.

This study introduces a novel electrochemical biosensor for detecting Matrix Metalloproteinase-2 (MMP-2), a key biomarker in cancer diagnostics and tissue remodeling. The biosensor is based on a dual-amplification strategy utilizing T7 RNA polymerase isothermal amplification and CRISPR-Cas12a technology. The principle involves the release of a DNA template in the presence of MMP-2, leading to RNA synthesis by T7 RNA polymerase. This RNA activates CRISPR-Cas12a, which cleaves a DNA probe on the electrode surface, resulting in a measurable electrochemical signal.The biosensor demonstrated exceptional sensitivity, with a detection limit of 2.62 fM for MMP-2. This high sensitivity was achieved through the combination of transcriptional amplification and the collateral cleavage activity of CRISPR-Cas12a, which amplifies the signal. The sensor was able to detect MMP-2 across a wide dynamic range from 2 fM to 1 nM, showing a strong linear correlation between MMP-2 concentration and the electrochemical signal. In practical applications, the biosensor accurately detected elevated levels of MMP-2 in cell culture supernatants from HepG2 liver cancer cells, distinguishing them from normal LO2 liver cells. The use of an MMP-2 inhibitor confirmed the specificity of the detection. These results underscore the biosensor\'s potential for clinical diagnostics, particularly in early cancer detection and monitoring of tissue remodeling activities. The biosensor\'s design allows for rapid, point-of-care testing without the need for complex laboratory equipment, making it a promising tool for personalized healthcare and diagnostic applications.

Rapid screening for foodborne pathogens is crucial for food safety. A rapid and one-step electrochemical sensor has been developed for the detection of Escherichia coli (E. coli), Staphylococcus aureus (S. aureus) and Salmonella typhimurium (S. typhimurium). Through the construction of aptamer/two-dimensional carboxylated Ti3C2Tx (2D C-Ti3C2Tx)/two-dimensional Zn-MOF (2D Zn-MOF) composites, the recognition elements, signal tags, and signal amplifiers are integrated on the electrode surface. Pathogens are selectively captured using the aptamer, which increases the impedance of the electrode surface，leads to a decrease in the 2D Zn-MOF current. Bacteria can be rapidly quantified using a one-step detection method and the replacement of aptamers. The detection limits for E. coli, S. aureus, and S. typhimurium are 6, 5, and 5 CFU·mL-1, respectively. The sensor demonstrated reliable detection capabilities in real-sample testing. Therefore, the one-step sensor based on the 2D Zn-MOF and 2D C-Ti3C2Tx has significant application value in the detection of foodborne pathogens.

Bisphenol A (BPA) has been widely used in the production of polycarbonate (PC) plastics, flame retardants and epoxy resins, which is one of the most important endocrine disrupting chemicals and can cause damage to the estrogen system of human. In this work, organic conjugated polymer nanoparticles (CPNPs) were synthesized through nanoprecipitation method using liposome 1,2-distearoyl-sn-glycero-3-phosphoethanolamine-N-[methoxy (polyethylene glycol)-2000] (DSPE-mPEG2000) coated poly[(4,4\'-bis(2-ethylhexyl)-dithieno[3,2-b:2\',3\'-d]silole)-2,6-diyl-alt-4,7-di(4-hexyl-2-thienyl)-5,6-difluoro-2,1,3-benzothiadiazole] (PDTS-hDTBT) and poly[(4,4\'-bis(2-ethylhexyl)-dithieno[3,2-b:2\',3\'-d]silole)-2,6-diyl-alt-4,7-di(4-(2-ethylhexyl)-2-thienyl)-5,6-difluoro-2,1,3-benzothiadiazole] (PDTS-ehDTBT). These two polymers have different side chains, which can affect the configuration of the polymers, thereby affecting the π-π interaction between BPA and CPNPs. The resultant two CPNPs were explored as extremely attractive matrix for tyrosinase immobilization to construct electrochemical biosensing platforms for sensitive and rapid detection of BPA in water environments. The electrochemical performance of these two biosensors was significantly enhanced, benefiting from the large specific surface area and excellent biocompatibility of CPNPs, as well as the strong π-π interaction between CPNPs and BPA. The current response of PDTS-ehDTBT-Tyr-Chi/GCE exhibited a good linear relationship with BPA concentration ranging from 0.02 to 3.0 μM with a low detection limit of 11.83 nM and a high sensitivity of 0.9724 μA μM-1 cm-2. The fabricated biosensor was further used for BPA detection in actual samples with a recovery rate of 92.0 %-99.4 %. With the remarkable advantages, CPNPs-based biosensor provides a highly sensitive detection tool for rapid detection of BPA in actual samples, which has broad application prospects.

Phoxim, extensively utilized in agriculture as an organothiophosphate insecticide, has the potential to cause neurotoxicity and pose human health hazards. In this study, an electrochemical enzyme biosensor based on Ti3C2 MXene/MoS2@AuNPs/AChE was constructed for the sensitive detection of phoxim. The two-dimensional multilayer structure of Ti3C2 MXene provides a robust framework for MoS2, leading to an expansion of the specific surface area and effectively preventing re-stacking of Ti3C2 MXene. Additionally, the synergistic effect of self-reduced grown AuNPs with MoS2 further improves the electrical conductivity of the composites, while the robust framework provides a favorable microenvironment for immobilization of enzyme molecules. Ti3C2 MXene/MoS2@AuNPs electrochemical enzyme sensor showed a significant response to phoxim in the range of 1 × 10-13 M to 1 × 10-7 M with a detection limit of 5.29 × 10-15 M. Moreover, the sensor demonstrated excellent repeatability, reproducibility, and stability, thereby showing its promising potential for real sample detection.

An electrochemical biosensor based on dual-amplified nucleic acid mode and biocatalytic silver deposition was constructed using catalytic hairpin assembly-hybrid chain reaction (CHA-HCR). The electrochemical detection of silver on the electrode by linear sweep voltammetry (LSV) can be utilized to quantitatively measure miR-205-5p since the amount of silver deposited on the electrode is proportional to the target nucleic acid. The current response values exhibit strong linearity with the logarithm of miR-205-5p concentrations ranging from 0.1 pM to 10 μM, and the detection limit is 28 fM. A consistent trend was found in the results of the qRT-PCR and electrochemical biosensor techniques, which were employed to determine the total RNA recovered from cells, respectively. Moreover, the constructed sensor was used to assess miR-205-5p on various cell counts, and the outcomes demonstrated the excellent analytical efficiency of the proposed strategy. The recoveries ranged from 97.85% to 115.3% with RSDs of 2.251% to 4.869% in human serum samples. Our electrochemical biosensor for miR-205-5p detection exhibits good specificity, high sensitivity, repeatability, and stability. It is a potentially useful sensing platform for tumor diagnosis and tumor type identification in clinical settings.

The residue of tobramycin, a broad spectrum antibiotic commonly used in animal husbandry, has evitable impact on human health, which may cause kidney damage, respiratory paralysis, neuromuscular blockade and cross-allergy in humans. Sensitive monitoring of tobramycin in animal-derived food products is therefore of great importance. Herein, a new aptamer electrochemical biosensor for sensing tobramycin with high sensitivity is demonstrated via exonuclease III (Exo III) and metal ion-dependent DNAzyme recycling and hybridization chain reaction (HCR) signal amplification cascades. Tobramycin analyte binds aptamer-containing hairpin probe to switch its conformation to expose the toehold sequence, which triggers Exo III-based catalytic digestion of the secondary hairpin to release many DNAzyme strands. The substrate hairpins immobilized on the Au electrode (AuE) are then cyclically cleaved by the DNAzymes to form ssDNAs, which further initiate HCR formation of lots of long methylene blue (MB)-tagged dsDNA polymers on the AuE. Subsequently electro-oxidation of these MB labels thus exhibit highly enhanced currents for sensing tobramycin within the 5-1000 nM concentration range with an impressive detection limit of 3.51 nM. Furthermore, this strategy has high selectivity for detecting tobramycin in milk and shows promising potential for detect other antibiotics for food safety monitoring.

Estrogen receptor alpha (ERα) serves as a crucial biomarker for early breast cancer diagnosis. In this study, we proposed an electrochemical aptasensor with nanomaterial carbon nanohorns/gold nanoparticle composites (1-AP-CNHs/AuNPs) as the substrate, and the primary amine groups on the antibody initiated the ring-opening polymerization (ROP) of monomer amino acid-ferrocene (NCA-Fc) on the electrode surface for ultrasensitive detection of ERα. The composite of 1-AP-CNHs/AuNPs not only possessed more active sites, but also increased the specific surface area of the electrode and allowed a large amount of ferrocene polymer long chains to be grafted onto the electrode surface to achieve signal amplification. Under optimal conditions, the detection limit of the method was 11.995 fg mL-1 with a detection range of 100 fg mL-1-100 ng mL-1. In addition, the biotin-streptavidin system was used to further improve the sensitivity of the sensor. Importantly, this approach could be applied for the practical detection of ERα in real samples.