Amplification-free gene expression analysis of formalin-fixed paraffin-embedded samples using scanning single-molecule counting.

In this paper, we present the applications of our newly developed, highly sensitive fluorescent detection method referred to as scanning single-molecule counting (SSMC). We found that the target RNA added to the total RNA was detected with high sensitivity at 384 aM by combining a magnetic bead-based assay and SSMC (MB-BA + SSMC). Gene expression analysis without reverse transcription or amplification confirmed that the pattern of gene expression was identical to that of real-time polymerase chain reaction (PCR). MB-BA + SSMC was also applied to formalin-fixed paraffin-embedded (FFPE) samples. RNA fragmentation and crosslinking owing to FFPE processing slightly affected gene expression. Conversely, FFPE samples showed an increase in gene Ct values and a decrease in the number of detectable genes when analyzed using real-time PCR. Overall, our results suggested that SSMC is a powerful tool for target RNA detection and amplification-free gene expression analysis.

Scanning single-molecule counting system for Eprobe with highly simple and effective approach.

Here, we report a rapid and ultra-sensitive detection technique for fluorescent molecules called scanning single molecular counting (SSMC). The method uses a fluorescence-based digital measurement system to count single molecules in a solution. In this technique, noise is reduced by conforming the signal shape to the intensity distribution of the excitation light via a circular scan of the confocal region. This simple technique allows the fluorescent molecules to freely diffuse into the solution through the confocal region and be counted one by one and does not require statistical analysis. Using this technique, 28 to 62 aM fluorescent dye was detected through measurement for 600 s. Furthermore, we achieved a good signal-to-noise ratio (S/N = 2326) under the condition of 100 pM target nucleic acid by only mixing a hybridization-sensitive fluorescent probe, called Eprobe, into the target oligonucleotide solution. Combination of SSMC and Eprobe provides a simple, rapid, amplification-free, and high-sensitive target nucleic acid detection system. This method is promising for future applications to detect particularly difficult to design primers for amplification as miRNAs and other short oligo nucleotide biomarkers by only hybridization with high sensitivity.