# Ultra-sensitive nanostructured electrochemical immunosensor for selective monitoring of L-phenylalanine in phenylketonuria patients

## TL;DR

A new electrochemical sensor can detect L-phenylalanine in blood samples with high accuracy, making it useful for phenylketonuria patients in remote areas.

## Contribution

A novel light-driven functionalization method and nanostructured electrode improve sensitivity and selectivity for L-phenylalanine detection.

## Key findings

- The sensor shows excellent linearity (R²=0.99) and low detection limits (LOD=0.3 µM) for L-phenylalanine.
- The sensor successfully quantifies L-phenylalanine in blood dry spots with agreement to mass spectrometry results.
- Integration with a portable potentiostat enables point-of-care and home use for PKU patients.

## Abstract

A low cost and rapid electrochemical immunosensor for direct screening of L-phenylalanine (L-Phe) using square wave voltammetry (SWV) is presented. Fern-like gold nanostructures were electro-deposited onto a screen-printed electrode (SPE) using chronoamperometry (CA), to enhance sensitivity and surface area. A novel light-driven surface functionalisation process was used to decorate the gold nanostructured SPE with target-specific antibody fragments and develop the L-Phe-specific immunosensor. The selectivity of the sensor was confirmed against tyrosine, tryptophan and D-phenylalanine, thus indicating the sensor’s potential for use at points of care (POC) without interference from structurally related biomolecules. The sensor demonstrated high sensitivity across the full clinical range (120 µM-1200 µM) and excellent linearity within the concentration range 1 µM to 2000 µM (R²= 0.99, LOD = 0.3 µM, LOQ = 1 µM). Quantification of L-Phe in human blood dry spots (DBS) by the new sensor and SWV were in excellent agreement with mass spectroscopy (MS) measurements by 2 independent pathology labs. The sensor was successfully integrated with an ultra-compact potentiostat in a Lab-on-a-Phone assembly for L-Phe screening in DBS, thus demonstrating its potential for use at POC and at home by phenylketonuria (PKU) patients in both remote and rural areas.

The online version contains supplementary material available at 10.1007/s00604-026-07836-8.