Optical Biosensor for Bacteremia detection from human blood samples at a label-free Liquid Crystal-Aqueous Interface: A Rapid and Point-of-Care approach

Detection of bacteremia requires recognizing bloodstream bacteria. Early identification of bacteremia is imperative for treatment and prevents the escalation to systemic infections like septicaemia. This paper introduces a novel, label-free biosensor based on liquid crystals (LCs), designed to offer rapid and reliable optical detection of blood pathogens without using traditional PCR methods. The biosensor utilizes 16S rRNA, a key structural component of the bacterial genome, as a molecular recognition probe. For accurate detection of target DNA, a nematic LC is positioned within a transmission electron microscopy (TEM) grid cell on a DMOAP-coated glass surface and treated with a cationic surfactant, cetyl trimethyl ammonium bromide (CTAB), to facilitate probe adhesion at the LC-aqueous interface. Initially, the CTAB-coated LC displays a homeotropic orientation, but it shifts to a planar/tilted orientation when the primer is added. Upon exposure to the target DNA, the LC returns to its homeotropic configuration, which can be observed using a polarizing optical microscope (POM) fitted with crossed polarizers. An optimal primer adsorption density of 100 nM allows detection of target DNA at concentrations as low as 0.02 nM. The biosensor has been verified for real-time, point-of-care utility by successfully detecting the genomic DNA of the bacterium E. coli cultured in human blood. The operational mechanism of this biosensor has also been confirmed using Circular Dichroism and Synchrotron X-ray Solution Scattering Measurements. Due to its high sensitivity and label-free nature, this biosensor provides a faster, more practical and user-friendly alternative to traditional pathogen detection methods from blood samples of bacteremia patients.