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Gold−platinum nanoparticles (AuPt NPs) were fabricated on chitosan (Ch)−ionic liquid (i.e., trihexyltetradecylphosphonium bis(trifluoromethylsulfonyl)imide, [P(C6)3C14][Tf2N]) film by using an ultrasonic electrodeposition method for the first time. Ch acted as an adsorbent for the metal ions, and [P(C6)3C14][Tf2N] played a dual role of matrix and stabilizer in the formation of the nanoparticles. The obtained AuPt NPs were characterized by scanning electron microscopy, X-ray photoelectron spectroscopy, and X-ray diffraction. It was found that they were well-dispersed on the composite surface, and their diameters were 10−20 nm. Furthermore, they exhibited the features of an alloy, and the atomic ratio of Au/Pt in the alloy NPs was close to the concentration ratio of AuCl4 −/PtCl6 2− in the solution. Electrochemical observation showed that the AuPt−Ch−[P(C6)3C14][Tf2N] modified glassy carbon electrode (GCE) had a large electroactive surface area and small electron transfer resistance. When the ratio of AuCl4 −/PtCl6 2− was around 3:1, the resulting electrode (i.e., Au3Pt1−Ch−[P(C6)3C14][Tf2N]/GCE) displayed high catalytic activity to the reduction of hydrogen peroxide (H2O2). Chronoamperometric experiments showed that at an applied potential of 0.05 V (vs SCE), the reduction current of H2O2 was linear to its concentration in the range of 5−355 nM, and the detection limit was found to be 0.3 nM on the basis of the signal-to-noise ratio of 3. The as-prepared nonenzyme hydrogen peroxide sensor exhibited excellent stability, repeatability, and selectivity.

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