A dual-signals fluorometric and colorimetric peptide-based probe for Cu(II) and glyphosate detection and its application for bioimaging and water testing

A novel dual-signal fluorometric and colorimetric probe FMDH (5-FAM-Met-Asp-His-NH₂), incorporating a tripeptide (Met-Asp-His-NH₂) linked to 5-carboxyfluorescein (5-FAM), was firstly synthesised. FMDH demonstrated exceptional selectivity and sensitivity, rapid response, wide pH response range and robust anti-interference capabilities for monitoring Cu²⁺. This was achieved through a distinctive naked-eye colorimetric and fluorescent quenching behaviour. A good linearity within the range of 0-3 μM (R² = 0.9914) was attained, and the limit of detection (LOD) for Cu²⁺ was 47.4 nM. Furthermore, the FMDH-Cu²⁺ ensemble responded to glyphosate with notable selectivity and sensitivity. A good linear correlation (R² = 0.9926) was observed at the lower concentration range (2.4-7.8 μM) and achieving a detection limit as low as 29.9 nM. The response time of FMDH with Cu²⁺ and glyphosate were less than 20 s, and the pH range of 7-11 that was suitable for practical application under physiological pH conditions. MTT assays confirmed that FMDH offers good permeability and low toxicity, facilitating successful application in imaging analysis of Cu²⁺ and glyphosate in living cells and zebrafish. In addition, FMDH was employed in the detection of these analytes in real water samples. Cost-effective, highly sensitive and easily prepared FMDH-impregnated test strips were developed for the efficient visual detection of Cu²⁺ and glyphosate under 365 nm UV light. Increasing concentrations of Cu²⁺ and glyphosate resulted in notable colour changes under 365 nm UV light, enabling visual semi-quantitative analysis via a smartphone colour-analysis App.