Nanophotonic Sialidase Immunoassay for Bacterial Vaginosis Diagnosis

Abstract

Bacterial vaginosis (BV) affects reproductive-age women and can lead to pelvic inflammatory disease, postpartum endometritis, and preterm labor/delivery and predisposes the infection of sexually transmitted diseases. Typically, BV diagnosis involves the analysis of vaginal swab samples via microscopy operated by highly skilled personnel. Hence, novel approaches for BV diagnosis are an existing need. In response, the first immunosensing platform targeting sialidase, a BV biomarker, is reported. The nanophotonic operational principle of this biosensing platform allows for a cheaper, faster, and simpler analysis when compared with an indirect enzyme-linked immunosorbent assay (ELISA). The clinical evaluation of such a nanotechnology is highlighted, where 162 vaginal swab samples were analyzed with high sensitivity and specificity (96.29%, respectively). The resulting nanoimmunosensing platform offers a resourceful approach to perform a timely BV diagnosis.

Figure 1

Schematic representation of the overall approach. (A) Sample collection, storage, and preparation. The sample is collected from the vaginal sac fundus with a sterile swap and placed in sodium chloride saline solution to be stored. The sample is then centrifuged to remove cellular waste, and the supernatant is aspirated to be analyzed. (B) Biosensing platform targeting SLD (nanoBV). The clinical sample is diluted (1:4) and mixed with the nanoconjugate (mAb-QDs) in a GO-coated microwell. Typically, negative samples (BV−) exhibit quenched nanoconjugates via nonradiative energy transfer due to the affinity between mAb-QDs and the GO-coated microwell. Generally, positive samples (BV+) exhibit a strong fluorescence, which can be quantified. This occurs because of the complex SLD/mAb-QDs has no affinity with the GO-coated microwell.

Figure 2

Analytical performance of the optimized SLD nanoimmunosensing system. (A) Kinetics of the fluorescence quenching corresponding to different concentrations of SLD. (B) Performance of nanoBV at specific times. (C) Calibration plot resulting at 120 min of the assay. The error bars represent the standard deviation of three parallel experiments.

Figure 3

Analysis of SLD levels in 162 clinical samples using nanoBV. The vaginal swab samples were classified in two groups according to Amsel criteria: bacterial vaginosis positive (BV+, n = 54 samples) and normal microbiota (NM, n = 108 samples). (A) Histogram of the resulting SLD levels in NM samples. (B) Histogram of the resulting SLD levels in BV+ samples. (C) Corresponding ROC curve depicting the high sensitivity and specificity of nanoBV. The area under the curve is 0.99.