Label-free bacteria detection using evanescent mode of a suspended core terahertz fiber

TL;DR

This paper introduces a novel label-free E. coli bacteria sensor using a suspended-core terahertz fiber's evanescent field, capable of detecting bacteria concentrations from 10^4 to 10^9 cfu/ml by monitoring absorption changes due to bacterial lysis.

Contribution

It is the first to utilize a suspended-core terahertz fiber with biofunctionalization for direct, label-free bacteria detection based on absorption changes from bacterial lysis.

Findings

Detects E. coli at 10^4-10^9 cfu/ml concentrations.

Demonstrates bacteria capture and lysis via SEM imaging.

Shows absorption increase correlates with bacterial presence.

Abstract

We propose for the first time an E. coli bacteria sensor based on the evanescent field of the fundamental mode of a suspended-core terahertz fiber. The sensor is capable of E. coli detection at concentrations in the range of 104-109 cfu/ml. The polyethylene fiber features a 150 {\mu}m core suspended by three deeply sub-wavelength bridges in the center of a 5.1 mm-diameter cladding tube. The fiber core is biofunctionalized with T4 bacteriophages which bind and eventually destroy (lyse) their bacterial target. Using environmental SEM we demonstrate that E. coli is first captured by the phages on the fiber surface. After 25 minutes, most of the bacteria is infected by phages and then destroyed with ~1{\mu}m-size fragments remaining bound to the fiber surface. The bacteria-binding and subsequent lysis unambiguously correlate with a strong increase of the fiber absorption. This signal allows the detection and quantification of bacteria concentration. Presented bacteria detection method is label-free and it does not rely on the presence of any bacterial "fingerprint" features in the THz spectrum.