Point-of-Care, Cable-Type Electrochemical Zn2+ Sensor with Ultrahigh Sensitivity and Wide Detection Range for Soil and Sweat Analysis

Achieving ultrahigh sensitivity over a wide concentration range of analyte has been a persistent, mutually exclusive challenge for real-time analytical detection and diagnostics. To this end, we demonstrate a miniaturized, coaxial, cable-type electrochemical sensor comprised of a carbon nanotube immobilized cellulose yarn (CNT-thread) to achieve ultrahigh sensitivity (<1 ppm) across a wide dynamic range (0.1–500 ppm) for the rapid (∼60 s) detection of Zn 2+ . The sensor comprises of two cables of CNT-thread, one coated with a polymeric, ion-receptor (tetrakis(p-aminophenyl) porphyrin) acting as the working electrode and the other being a reference electrode of pristine CNT-thread. The sensor is extremely tolerant to interference (selectivity coefficient 10 –3 –10 –5 ) from a wide range of cations (Na +, K +, Mg 2+, Cd 2+, Ca 2+, Fe 2+, and Cu 2+ ) and anions (Cl –, NO 3 –, PO 4 3–, and CH 3 COO – ) enabling real-time detection of Zn 2+ across varied spectrum of samples ranging from human perspiration to agricultural soil. Importantly, excellent signal consistency (<5% deviation) across multiple electrochemical techniques such as cyclic voltammetry, differential pulse voltammetry, and chronoamperometry is demonstrated. Minimal deviation (<6%) between the analyte concentrations estimated from the sensor and those estimated from atomic-absorption techniques is observed. Further, such ultrasensitive detection of Zn 2+ over a 5000-fold concentration range is critical for both medical diagnostics (muscular stress) and soil-nutrient assessment (scientific farming). Such a single platform that is capable of handling such diverse real-time applications has not been demonstrated earlier. Finally, the lifetime and mechanical sturdiness of the sensing platform is illustrated through elaborate experiments involving bending and seamless interfacing with human skin for noninvasive point-of-care analysis.