# Intermolecular Structure Conversion-Based G4-TDF Nanostructures Functionalized μPADs for Fluorescent Determination of Potassium Ion in Serum

## TL;DR

This paper introduces a new paper-based device that uses DNA nanostructures to detect potassium ions in human serum with high sensitivity and accuracy.

## Contribution

The novel contribution is the first application of G4-TDF nanostructures on μPADs for fluorescent K+ detection with low detection limits and high specificity.

## Key findings

- The G4-TDF nanostructure on μPADs achieved a detection limit of 0.2 mM for potassium ions.
- The device demonstrated excellent specificity and a wide detection range of 0.5–5.5 mM.
- The method was successfully applied to detect potassium ions in human serum samples.

## Abstract

Herein, we proposed a versatile G-quadruplex (G4)-tetrahedral DNA framework (G4-TDF) nanostructure functionalized origami microfluidic paper-based device (μPADs) for fluorescence detection of K+ by lighting up thioflavin T (ThT). In this work, TDF provided robust structural support for G-rich sequence in well-defined orientation and spacing to ensure high recognition efficiency, enabling sensitive fluorescence sensing on origami μPAD. After introducing ThT, the G-rich sequences extended from TDF vertices formed a parallel G4 structure, showing weak fluorescence signal output. Upon the presence of target K+, this parallel G4 structure transitioned to antiparallel G4 structure, leading to a significantly increase in fluorescence signal of ThT. Benefiting from the outstanding fluorescence enhancement characteristic of the G4 structure for ThT and excellent specificity of the G4 structure to K+ plus satisfactory recognition efficiency with the aid of TDF, this origami paper-based fluorescence sensing strategy exhibited an impressive detection limit as low as 0.2 mM with a wide range of 0.5–5.5 mM. This innovative G4-TDF fluorescence sensing was applied for the first time on μPAD, providing a simple, effective, and rapid method for K+ detection in human serum with significant potential for clinical diagnostics.