Leaky waveguide sensor platform for rapid reagent-free microbial detection

Overview

This solution addresses the need for rapid, reagent-free detection of low numbers of microbes in liquid samples. It combines ultrasound waves, which actively transport microbial cells to a sensor surface, with leaky waveguide (LW) sensors that detect captured cells through evanescent wave scattering. By co-locating a low sound pressure region with the waveguide surface, microbes are concentrated on the sensor where their higher refractive index relative to the surrounding medium produces a detectable optical signal. The approach aims to deliver sensitive microbial detection in minutes, supporting applications such as water quality monitoring, food safety testing, clinical diagnostics, and bioprocess control where timely results are critical.

Technical specifications

• Ultrasound-driven transport: Sound waves move microbial cells toward low sound pressure regions positioned at the waveguide surface, enabling active accumulation without chemical reagents.
• Leaky waveguide evanescent scattering: LWs generate an evanescent field with a penetration depth of a few microns, allowing detection of relatively large microbes captured on the surface via scattering of the evanescent wave.
• Hydrogel waveguide design: Planned LWs made from hydrogel materials to reduce optical losses and produce high-intensity evanescent fields with larger penetration depth for improved sensitivity.
• Surface capture elements: Hydrogel surfaces will be modified with recognition elements that selectively bind target microbes, enhancing capture efficiency at the sensor interface.
• Microfluidic flow cell integration: A purpose-built flow cell ensures samples pass through a single low sound pressure region coincident with the LW surface, maximising transport of particles to the detection zone.
• Optimised instrumentation: Signal collection is designed to occur from beneath the waveguide and substrate, allowing ultrasound transducers to be placed directly above the detection region for improved microbial transport.
• Prior benchmark: Earlier work demonstrated a limit of detection of at least 10^3 cells/ml with an analysis time of approximately 3 minutes, establishing the feasibility of the integrated approach.

Technology readiness level

The technology is at an early-to-mid stage of development. Prior proof-of-concept work has demonstrated the core principle of ultrasound-integrated leaky waveguide detection, achieving detection of 10^3 cells/ml within 3 minutes. However, that earlier implementation used waveguide materials and metal films that produced high optical losses, lacked recognition elements for microbial capture, and employed non-optimal instrumentation and flow cell design. Current and planned work focuses on addressing each of these limitations through hydrogel waveguide development, surface functionalisation with recognition elements, microfluidic flow cell optimisation, and redesigned signal collection and transducer placement. The platform is not yet commercially available and requires further validation to confirm improved sensitivity and readiness for deployment in real-world settings.