# Surface-Imprinted Polymer Coupled with Diffraction Gratings for Low-Cost, Label-Free and Differential E. coli Detection

## TL;DR

A new sensor uses polymer and light patterns to detect E. coli quickly and inexpensively without labels.

## Contribution

A photolithography-based SIP sensor with built-in diffraction gratings for label-free bacterial detection.

## Key findings

- High-density cavity arrays (3 × 10⁷ imprints/cm²) improve imprint uniformity and reproducibility.
- Differential detection of E. coli in PBS shows concentration-dependent sensitivity.
- FDTD simulations confirm optical response changes upon bacterial binding.

## Abstract

Surface-imprinted polymer (SIP)-based biomimetic sensors are promising for direct whole-bacteria detection; however, the commonly used fabrication approach (micro-contact imprinting) often suffers from limited imprint density, heterogeneous template distribution, and poor reproducibility. Here, we introduce a photolithography-defined master stamp featuring E. coli mimics, enabling high-density, well-oriented cavity arrays (3 × 107 imprints/cm2). Crucially, the cavity arrangement is engineered such that the SIP layer functions simultaneously as the bioreceptor and as a diffraction grating, enabling label-free optical quantification by reflectance changes without additional transduction layers. Finite-difference time-domain (FDTD) simulations are used to model and visualize the optical response upon bacterial binding. Proof-of-concept experiments using a differential two-well configuration confirm concentration-dependent detection of E. coli in PBS, demonstrating a sensitive, low-cost, and scalable sensing concept that can be readily extended to other bacterial targets by redesigning the photolithographic master.