Kill two birds with one stone: Ratiometric sensing of phosphate via a single-component probe with fluorescence-scattering dual-signal response behavior

Abstract

Ratiometric fluorescence sensors gain stronger anti-interference ability via self-calibration. Nevertheless, ratiometric analysis of phosphate (Pi) still faces problems such as complicated construction process of dual emission probes and possible interferences from outputting mono-category fluorescent signal. Herein, we propose a "kill two birds with one stone" strategy to address these challenges, by simply introducing a single-component probe, porphyrin paddlewheel framework-3 (PPF-3) nanosheets without modification, encapsulation or complex, to integrate fluorescence (FL)-second-order scattering (SOS) dual-signal for ratiometric detection of Pi. PPF-3 nanosheets are constructed by coordination of Co²⁺ with 5,10,15,20-tetrakis(4-carboxyl-phenyl)-porphyrin (TCPP) ligands, displaying weak FL and strong SOS, two different and independent signals. In the response system to Pi, Co²⁺ and TCPP serve as the recognition element and signal unit, respectively. After interacting with Pi, the high affinity for Co²⁺ makes Pi snatch Co²⁺ from the PPF-3 nanosheets, causing their structure disassembly (SOS decrease) and TCPP release (FL increase). Finally, the FL-SOS ratiometric platform is successfully employed to access Pi in real water samples. Synchronous collection of FL and SOS from the single-component probe provides a simpler and more efficient way on ratiometric sensor design as well as a new useful technique for monitoring target-induced aggregation and disaggregation behavior.

Keywords: Fluorescence; Phosphate; Porphyrin paddlewheel framework-3 (PPF-3) nanosheets; Ratiometric sensor; Second-order scattering; Single-component probe.