A microfluidic multiwell chip for enzyme-free detection of mRNA from few cells

One-step fabrication of trimetallic alloy nanozyme catalyzer for luminol-H2O2 chemiluminescence and its application for miRNA-21 detection coupled with miRNA walking machine

PtCuCo trimetallic alloys (PtCuCo-TAs) are synthesized by one-step reduction. The chemiluminescence (CL) properties of PtCuCo-TAs are studied systemically. PtCuCo-TAs show good catalyzing for luminol-H₂O₂ system. A CL platform is developed for the detection of miRNA-21 using PtCuCo-TAs as nanozyme catalyzer. In the CL detection platform, H1 (Hairpin DNA1) is immobilized onto magnetic beads (MBs) firstly. In the presence of miRNA-21, H1 is opened. H2 (Hairpin DNA2) then hybridizes with H1. Meanwhile, a "cleat" in the end of miRNA-21 with a fewer bases complementary is formed to prevent miRNA-21 dissociating from H1. This miRNA-21 hybridizes to another H1. When cpDNA-PtCuCo-TAs which consisted with cDNA (Complementary strand of probe DNA) and pDNA-PtCuCo-TAs (PtCuCo-TAs labeled with probe DNA) are added, the ssDNA region of H1 reacts with the toehold domain of probe DNA and cDNA is released resulting pDNA-PtCuCo-TAs being captured. With this process repeatedly, a lot of pDNA-PtCuCo-TAs are captured onto MBs. After separation and washing, the precipitate and H₂O₂ are put into the 96-well and luminol solution is injected. The CL signal is produced by PtCuCo-TAs catalyzing luminol-H₂O₂ system. The amount of miRNA-21 is detected with CL signal. This CL platform performs with limit of detection 0.167 fM and has good selectivity over other RNA.

EGFR point mutation detection of single circulating tumor cells for lung cancer using a micro-well array

In view of their critical function in metastasis, characterization of single circulating tumor cells (CTCs) can provide important clinical information to monitor tumor progression and guide personal therapy. Single-cell genetic analysis methods based on microfluidics have some inherent shortcomings such as complicated operation, low throughput, and expensive equipment requirements. To overcome these barriers, we developed a simple and open micro-well array containing 26,208 units for either nuclear acids or single-cell genetic analysis. Through modification of the polydimethylsiloxane surface and optimization of chip packaging, we addressed protein adsorption and solution evaporation for PCR amplification on a chip. In the detection of epidermal growth factor receptor (EGFR) exon gene 21, this micro-well array demonstrated good linear correlation at a DNA concentration from 1 × 10¹ to 1 × 10⁵ copies/μL (R² = 0.9877). We then successfully integrated cell capture, lysis, PCR amplification, and signal read-out on the micro-well array, enabling the rapid and simple genetic analysis of single cells. This device was used to detect duplex EGFR mutation genes of lung cancer cell lines (H1975 and A549 cells) and normal leukocytes, demonstrating the ability to perform high-throughput, massively parallel duplex gene analysis at the single-cell level. Different types of point mutations (EGFR-L858R mutation or EGFR-T790M mutation) were detected in single H1975 cells, further validating the significance of single-cell level gene detection. In addition, this method showed a good performance in the heterogeneity detection of individual CTCs from lung cancer patients, required for micro-invasive cancer monitoring and treatment selection.

Digital Microarrays: Single-Molecule Readout with Interferometric Detection of Plasmonic Nanorod Labels

DNA and protein microarrays are a high-throughput technology that allow the simultaneous quantification of tens of thousands of different biomolecular species. The mediocre sensitivity and limited dynamic range of traditional fluorescence microarrays compared to other detection techniques have been the technology's Achilles' heel and prevented their adoption for many biomedical and clinical diagnostic applications. Previous work to enhance the sensitivity of microarray readout to the single-molecule ("digital") regime have either required signal amplifying chemistry or sacrificed throughput, nixing the platform's primary advantages. Here, we report the development of a digital microarray which extends both the sensitivity and dynamic range of microarrays by about 3 orders of magnitude. This technique uses functionalized gold nanorods as single-molecule labels and an interferometric scanner which can rapidly enumerate individual nanorods by imaging them with a 10× objective lens. This approach does not require any chemical signal enhancement such as silver deposition and scans arrays with a throughput similar to commercial fluorescence scanners. By combining single-nanoparticle enumeration and ensemble measurements of spots when the particles are very dense, this system achieves a dynamic range of about 6 orders of magnitude directly from a single scan. As a proof-of-concept digital protein microarray assay, we demonstrated detection of hepatitis B virus surface antigen in buffer with a limit of detection of 3.2 pg/mL. More broadly, the technique's simplicity and high-throughput nature make digital microarrays a flexible platform technology with a wide range of potential applications in biomedical research and clinical diagnostics.

Optical transformation of a CdTe quantum dot-based paper sensor for a visual fluorescence immunoassay induced by dissolved silver ions

This work designs a visual fluorescence immunoassay for carcinoembryonic antigen based on structural and optical transformation of CdTe quantum dots immobilized on paper by cation-exchange reaction.