Fast synthesis of platinum nanopetals and nanospheres for highly-sensitive non-enzymatic detection of glucose and selective sensing of ions

Abstract

Novel methods to obtain Pt nanostructured electrodes have raised particular interest due to their high performance in electrochemistry. Several nanostructuration methods proposed in the literature use costly and bulky equipment or are time-consuming due to the numerous steps they involve. Here, Pt nanostructures were produced for the first time by one-step template-free electrodeposition on Pt bare electrodes. The change in size and shape of the nanostructures is proven to be dependent on the deposition parameters and on the ratio between sulphuric acid and chloride-complexes (i.e., hexachloroplatinate or tetrachloroplatinate). To further improve the electrochemical properties of electrodes, depositions of Pt nanostructures on previously synthesised Pt nanostructures are also performed. The electroactive surface areas exhibit a two order of magnitude improvement when Pt nanostructures with the smallest size are used. All the biosensors based on Pt nanostructures and immobilised glucose oxidase display higher sensitivity as compared to bare Pt electrodes. Pt nanostructures retained an excellent electrocatalytic activity towards the direct oxidation of glucose. Finally, the nanodeposits were proven to be an excellent solid contact for ion measurements, significantly improving the time-stability of the potential. The use of these new nanostructured coatings in electrochemical sensors opens new perspectives for multipanel monitoring of human metabolism.

Figure 1. Morphology of electrodeposited Pt films after experiment I, II, III, IV.

Figure 2

SEM images of Pt coatings obtained at different deposition times (bars: 200 nm) (a). Evolution of the electroactive area with deposition time (potential: −1 V; solution: 25 mM H₂PtCl₆ and 50 mM H₂SO₄) (b).

Figure 3

SEM images of Pt electrodeposited by applying −0.2 V for 90 s (a) or 200 s (b), and −1 V for 90 s (c) or 200 s (d), from solutions containing 25 mM K₂PtCl₄ and 50 mM H₂SO₄ (e).

Figure 4. SEM images of Pt nanoflowers electrodeposited on nanospheres.

Figure 5

CVs at 20 mV/s of electrodes modified with nanopetals ((a) in blue; −1 V; 200 s, tetravalent Pt-based solution) and with nanospheres ((b) in red; −0.2 V; 200 s, divalent Pt-based solution) in solutions containing PBS without (dotted line) and with (straight line) 20 mM glucose. Square wave voltammetries (SWVs) at 15 mV/s in cell media containing glucose concentrations equal to 4, 8, 12, 16, 20 mM and respective calibration curve (estimation of standard deviation from duplicate measurements) (c). Sensitivities to glucose detection of enzyme-based electrodes without and with nanostructures, namely, Pt nanospheres (−0.2 V; 200 s, Pt-based solution), Pt nanopetals (−1 V; 200 s, tetravalent Pt-based solution), and Pt nanopetals (−1 V; 90 s, tetravalent Pt-based solution) grown on Pt nanospheres (−0.2 V; 200 s, divalent Pt-based solution). Error bars refer to the standard error of inter-sample triplicate measurements (d).

Figure 6

Water-layer test for Pt-K⁺/ISM electrode (green line), Pt nanospheres-K⁺-ISM electrode (red line; −0.2 V for 200 s from divalent Pt-based solution) and Pt nanopetals-K⁺-ISM electrode (blue line; −1 V; 200 s, tetravalent Pt-based solution) (a). RCP for Pt-K⁺/ISM electrode (green line), Pt nanospheres-K⁺-ISM electrode (red line) and Pt nanopetals-K⁺-ISM electrode (blue line). The applied current was +5 nA for 60 s and −5 nA for 60 s in 0.1 mM KCl (b). Calibration plot (in green) of the solid-contact K⁺-selective electrode based on Pt nanostructured electrode (c).