# Advancing the Development of Subcutaneous Glucose Biosensors: Cargo‐Carrying Adhesive Biosensor Systems (CABs)

## TL;DR

Researchers developed a new type of subcutaneous glucose biosensor that can store and retain small assay molecules using a novel adhesive design.

## Contribution

The CAB system introduces a new method for housing optical-assay molecules using electrostatic adhesion and dual-network hydrogels.

## Key findings

- CABs successfully retained small molecules with hydrodynamic diameters of ~7 nm and ~10 nm.
- The CAB wall composition provided thermosensitivity, mechanical robustness, and low mesh size.
- Electrostatic adhesion between anionic and cationic components enabled stable biosensor assembly.

## Abstract

The development of an injectable, subcutaneous glucose biosensor may be advanced by utilizing optical glucose sensing assays. However, this requires a strategy to effectively house small‐sized assay molecules. Herein, “CABs” or cargo‐carrying adhesive biosensors were constructed via the electrostatic adhesion of a hollow rod membrane (whose cavity could store a liquid optical‐assay) and hydrogel caps. For the CAB ‘wall’, the hollow rod leveraged a comb double network (DN) design previously shown to limit biofouling and reduce mesh size. To regulate the mesh size, poly(AMPS)‐methacrylate (PAMPSn‐MA) comb macromers were incorporated into the 1st network. To improve electrostatic adhesivity, anionic 2‐acrylamido‐2‐methylpropane sulfonic acid (AMPS) was incorporated into the second network of the DN hydrogels at varying concentrations. For the CAB ‘cap’ with a cationic surface, a semi‐interpenetrating polymer network was formed, comprised of crosslinked polyampholyte and non‐crosslinked cationic polyelectrolyte. A CAB was constructed with a CAB wall based on a DN hydrogel composition shown to exhibit the requisite thermosensitivity, mechanical robustness, glucose diffusivity, low mesh size (4 nm < ξ < 7 nm), and adhesivity to the CAB cap. Using FITC‐dextran solutions, the CAB was shown to retain ∼90% of molecules of low hydrodynamic diameters (Dh ∼ 7 nm and Dh
 ∼ 10 nm).

A “CAB” or “cargo‐carrying adhesive biosensor” was constructed by leveraging electrostatic adhesion between an anionic hollow rod membrane (whose cavity could store a liquid optical‐assay) and cationic hydrogel caps. A final CAB was constructed from the optimal CAB wall candidate and CAB cap, and successfully retained small molecules (hydrodynamic diameter: ∼7 and ∼10 nm) within the central cavity.