Size-tunable copper nanocluster aggregates and their application in hydrogen sulfide sensing on paper-based devices

Abstract

Polystyrene sulfonate (PSS), a strong polyelectrolyte, was used to prepare red photoluminescent PSS-penicillamine (PA) copper (Cu) nanoclusters (NC) aggregates, which displayed high selectivity and sensitivity to the detection of hydrogen sulfide (H2S). The size of the PSS-PA-Cu NC aggregates could be readily controlled from 5.5 μm to 173 nm using different concentrations of PSS, which enabled better dispersity and higher sensitivity towards H2S. PSS-PA-Cu NC aggregates provided rapid H2S detection by using the strong Cu-S interaction to quench NC photoluminescence as a sensing mechanism. As a result, a detection limit of 650 nM, which is lower than the maximum level permitted in drinking water by the World Health Organization, was achieved for the analysis of H2S in spring-water samples. Moreover, highly dispersed PSS-PA-Cu NC aggregates could be incorporated into a plate-format paper-based analytical device which enables ultra-low sample volumes (5 μL) and feature shorter analysis times (30 min) compared to conventional solution-based methods. The advantages of low reagent consumption, rapid result readout, limited equipment, and long-term storage make this platform sensitive and simple enough to use without specialized training in resource constrained settings.

Figure 1

(a) Photographs of the PSS-PA-Cu NC aggregates synthesized under different concentrations of PSS, from 0.005–0.5 wt%. The upper row is shown under daylight and the bottom row is under UV illumination. (b) DLS analysis and (c) zeta-potential of PSS-PA-Cu NC aggregates in the presence of different concentrations of PSS from 0.005–0.5 wt%. (d) A scheme depicting a plausible mechanism for how PSS stabilizes PA-Cu NC aggregates.

Figure 2. Excitation (black dotted line) and emission spectra (black solid line) of PSS-PA-Cu NCs.

The excitation and emission wavelengths were 325 nm and 665 nm, respectively.

Figure 3. The photostability of PSS-PA-Cu NC aggregates (0.05×) and PA-Cu NC aggregates (0.05×) prepared in sodium phosphate buffer solutions (pH 3.0, 10 mM).

The excitation wavelength was 325 nm.

Figure 4

(a) PL spectra of PSS-PA-Cu NC aggregates (0.05×) as a function of H₂S. Inset to (a): Linear plot [(I_PL0 − I_PL)/I_PL0] of the PSS-PA-Cu NC aggregates against H₂S concentration in sodium phosphate buffer solutions (10 mM, pH 3.0). (b) Selectivity of the PSS-PA-Cu NC aggregates (0.05×) toward H₂S over other anions. The concentrations of S²⁻ and CN⁻ were 20 μM; other potential interference ions were at a concentration of 100 μM. Mixtures were prepared in sodium phosphate buffer solutions (10 mM, pH 3.0). I_PL0 and I_PL are the PL intensities at 665 nm of the PSS-PA-Cu NC aggregates in the absence and presence of the potential interference ion, respectively.

Figure 5

(a) A representative scheme for the detection of H₂S on a PSS-PA-Cu NC/μPAD device. (b) Photographs of an on/off PSS-PA-Cu NC/μPAD for determination of the existence of H₂S in Beitou hot spring-water samples for determination by the naked-eye. The control sample was phosphate buffer solution (pH 3.0, 10 mM) in the absence of H₂S. (c) The upper row is the change in PL intensity of PSS-PA-Cu NC/μPADs at various H₂S concentrations recorded by a smartphone. The lower row is the relative PL intensity plot [(I_PL0 − I_PL)/I_PL0] of the PSS-PA-Cu NC/μPAD at 665 nm as a function of H₂S. Inset: Linear plot [(I_PL0 − I_PL)/I_PL0] of the PSS-PA-Cu NC aggregates against H₂S concentration. The light source in (b,c) was a hand-held UV lamp.