In this work, we report the synthesis and characterization of a bimetallic Prussian blue analogue containing Co and Mn as outer-sphere metals (CoMnHCF). The material was a solid solution and its characterization revealed a chemical composition of Co 2.05 Mn 0.95 [Fe(CN) 6 ] 2 · 12H 2 O. The electrochemistry of this novel material showed the existence of two redox waves displaying quasi-reversible kinetics, as expressed by the larger peak-to-peak separation upon increasing the potential sweep rate. Interestingly, the CoMnHCF solid exhibited high electrocatalytic activity for the oxidation of hydrogen peroxide, thus representing an appealing scaffold for the construction of biosensors. As a proof of concept, cholesterol oxidase was immobilized at the electrode surface by using a sol-gel method, and the cyclic voltammograms were recorded at increasing concentrations of cholesterol. The biosensor showed a detection limit of 30 μM and two linear ranges with excellent sensitivity of 385 mA cm À 2 M À 1 between 50 and 150 μM, and an adequate sensitivity of 80 mA cm À 2 M À 1 between 150 and 1 mM. To the best of our knowledge, this is the first biosensor application of a pre-synthesized bimetallic hexacyanometallate, thus exploiting its potential as an H 2 O 2 electrooxidation catalyst.

The antigenicity of three chimeric synthetic peptides (Qm, Qm-16, and Qm-17) incorporating an immunodominant epitope of the gp41 transmembrane protein (587-617) and the different epitopes of the gp120 envelope protein (495-516), (301-335), (502-516) of human immunodeficiency virus (HIV-1), separated by two glycine residues, was evaluated by UltramicroEnzyme-linked immunosorbent assay (UMELISA) by using panels of anti-HIV-1 positive sera (n = 47). The specificity was evaluated with samples from healthy blood donors (n = 20) and anti-HIV-2 positive samples (n = 10). The results indicate that the chimeric peptide, Qm, was the most reactive one because it detected antibodies to virus efficiently. This may be related to peptide adsorption onto the solid surface, the C-terminal region of HIV-1 gp120 (495-516) combined with gp41 (587-617) in the chimera, and the epitope accessibility to the antibodies. This study showed the usefulness of the chimeric peptides as antigen to detect antibodies to HIV-1 virus.

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