Affinity Immobilization of Semiconductor Quantum Dots and Metal Nanoparticles on Cellulose Paper Substrates

Quantum Dot-Based Molecular Beacons for Quantitative Detection of Nucleic Acids with CRISPR/Cas(N) Nucleases

Strategies utilizing the CRISPR/Cas nucleases Cas13 and Cas12 have shown great promise in the development of highly sensitive and rapid diagnostic assays for the detection of pathogenic nucleic acids. The most common approaches utilizing fluorophore-quencher molecular beacons require strand amplification strategies or highly sensitive optical setups to overcome the limitations of the readout. Here, we demonstrate a flexible strategy for assembling highly luminescent and colorimetric quantum dot-nucleic acid hairpin (QD-HP) molecular beacons for use in CRISPR/Cas diagnostics. This strategy utilizes a chimeric peptide-peptide nucleic acid (peptide-PNA) to conjugate fluorescently labeled DNA or RNA hairpins to ZnS-coated QDs. QDs are particularly promising alternatives for molecular beacons due to their greater brightness, strong UV absorbance with large emission offset, exceptional photostability, and potential for multiplexing due to their sharp emission peaks. Using Förster resonance energy transfer (FRET), we have developed ratiometric reporters capable of pM target detection (without nucleotide amplification) for both target DNA and RNA, and we further demonstrated their capabilities for multiplexing and camera-phone detection. The flexibility of this system is imparted by the dual functionality of the QD as both a FRET donor and a central nanoscaffold for arranging nucleic acids and fluorescent acceptors on its surface. This method also provides a generalized approach that could be applied for use in other CRISPR/Cas nuclease systems.

Electrochemical Biosensors for Circulating Tumor DNA Detection

Early diagnosis and treatment have always been highly desired in the fight against cancer, and detection of circulating tumor DNA (ctDNA) has recently been touted as highly promising for early cancer-screening. Consequently, the detection of ctDNA in liquid biopsy is gaining much attention in the field of tumor diagnosis and treatment, which has also attracted research interest from industry. However, it is difficult to achieve low-cost, real-time, and portable measurement of ctDNA in traditional gene-detection technology. Electrochemical biosensors have become a highly promising solution to ctDNA detection due to their unique advantages such as high sensitivity, high specificity, low cost, and good portability. Therefore, this review aims to discuss the latest developments in biosensors for minimally invasive, rapid, and real-time ctDNA detection. Various ctDNA sensors are reviewed with respect to their choices of receptor probes, designs of electrodes, detection strategies, preparation of samples, and figures of merit, sorted by type of electrode surface recognition elements. The development of biosensors for the Internet of Things, point-of-care testing, big data, and big health is analyzed, with a focus on their portable, real-time, and non-destructive characteristics.