Oligonucleotide-Driven Nanoparticle Biosensor for <i>Candida albicans</i> Detection in Vaginal Swabs

Vulvovaginal candidiasis (VVC), caused by <i>Candida albicans</i> <i>(</i> <i>C.albicans</i> <i>)</i>, is a common gynecological infection. VVC is traditionally diagnosed using microbiological culture and microscopy by immunofluorescence, which suffer from limitations such as time-consuming procedures and subjectivity. This study developed a colorimetric biosensor based on gold nanoparticles functionalized with oligonucleotides for the rapid detection of <i>C.albicans</i>. To target the specific hypha wall protein 1 gene (HWP1), thiol-modified oligonucleotide probes were designed and conjugated to the surface of 60 nm citrate-stabilized gold nanoparticles (AuNPs). When the target RNA is present, oligonucleotide hybridization induces nanoparticle aggregation, causing a color shift in the solution from red to transparent, which can be quantitatively detected using UV-visible spectrophotometry. Experimental optimization of salt concentration for hybridization determined the optimal condition as 7 μL of 5 M NaCl, with a limit of detection calculated via the 3σ/slope method of 0.078 nM. Clinical validation using 234 vaginal swab samples provided by Ruijin Hospital (Shanghai, China) demonstrated an achieved sensitivity of 85.0%, specificity of 85.4%, and overall accuracy of 85.3%. Besides, the entire detection process was completed within 40 min without enzymatic amplification. This AuNP-based colorimetric sensor offers advantages of rapidity, low cost, high sensitivity, and specificity, providing an efficient novel method for the early diagnosis of VVC.