# A Visual Raman Nano−Delivery System Based on Thiophene Polymer for Microtumor Detection

## TL;DR

This paper introduces a new thiophene-based polymer for Raman imaging that improves tumor detection by enabling deep tissue visualization with minimal interference.

## Contribution

A donor–acceptor thiophene polymer, PBDB-T, is developed for enhanced near-infrared Raman imaging of microtumors.

## Key findings

- PBDB-T achieves ultra-strong Raman enhancement under 785 nm excitation without fluorescence interference.
- The PBDB-T system successfully detects microtumors as small as 0.5 mm × 0.9 mm in vivo.
- The polymer has an in vivo circulation half-life of 14.5 hours, enabling deep tumor tissue diagnosis.

## Abstract

A visual Raman nano-delivery system (NS) is a widely used technique for the visualization and diagnosis of tumors and various biological processes. Thiophene-based organic polymers exhibit excellent biocompatibility, making them promising candidates for development as a visual Raman NS. However, materials based on thiophene face limitations due to their absorption spectra not matching with NIR (near-infrared) excitation light, which makes it difficult to achieve enhanced Raman properties and also introduces potential fluorescence interference. In this study, we introduce a donor–acceptor (D-A)-structured thiophene-based polymer, PBDB-T. Due to the D-A molecular modulation, PBDB-T exhibits a narrow bandgap of Eg = 2.63 eV and a red-shifted absorption spectrum, with the absorption edge extending into the NIR region. Upon optimal excitation with 785 nm light, it achieves ultra-strong pre-resonant Raman enhancement while avoiding fluorescence interference. As an intrinsically sensitive visual Raman NS for in vivo imaging, the PBDB-T NS enables the diagnosis of microtumor regions with dimensions of 0.5 mm × 0.9 mm, and also successfully diagnoses deeper tumor tissues, with an in vivo circulation half-life of 14.5 h. This research unveils the potential application of PBDB-T as a NIR excited visual Raman NS for microtumor diagnosis, introducing a new platform for the advancement of “Visualized Drug Delivery Systems”. Moreover, the aforementioned platform enables the development of a more diverse range of targeted visual drug delivery methods, which can be tailored to specific regions.