Owing to fast SARS-CoV-2 mutations, biosensors employing antibodies as biorecognition elements have presented problems with sensitivity and accuracy. To face these challenges, antibodies can be replaced with the human angiotensin converting enzyme 2 (ACE-2), where it has been shown that the affinity between ACE-2 and the receptor binding domain (RBD) increases with the emergence of new variants. Herein, we report on Ni-doped ZnO nanorod electrochemical biosensors employing an ACE-2 peptide (IEEQAKTFLDKFNHEAEDLFYQS-NH₂) as a biorecognition element for detecting Spike (S) Wild-Type (WT) protein. The electrode was fully characterized in terms of electrochemical and physical properties. The sensor showed high cross reactivity with Spike protein B.1.1.7 and Spike protein B.1.351. Still, there was no cross reactivity with the Nucleocapsid protein WT, showing that the biosensor can identify ancestral WT S protein and S protein variants of concern. The device exhibited a LOD of 60.13 ng mL^-1 across an S protein WT concentration range from 200 ng mL^-1 to 1000 ng mL^-1 and a LOQ of 182.22 ng mL^-1. The calculated sensitivity and specificity were 88.88 and 100 %, respectively. These results proved that the Ni-ZnO sensor has promising prospects for SARS-CoV-2 detection and diagnosis of other viruses, employing peptides as biorecognition elements.

Background: Peptides are promising tools in medicine for viral, bacterial, and parasitic infections. MAP1 and MAP2 are peptides with antimicrobial activity. Aiming to increase selectivity, enhance antimicrobial activity, and reduce its cytotoxicity, two bioconjugates (GVL1-MAP2 and GVL1-MAP1) with the guanidine derivative group in the N-terminus position were synthesized. Methods: The peptides and bioconjugates were synthesized by SPPS. The biological activity and inhibition of the CPB enzyme were evaluated. Results: Antileishmanial activity was evaluated, and the bioconjugates exhibited higher activity in both the promastigote and amastigote forms than isolated GVL1 and peptides alone. Discussion: GVL1-MAP2 bioconjugate demonstrated not only the greatest activity against L. amazonensis in the promastigote (IC₅₀ = 3.2 μM) and amastigote (IC₅₀ = 0.6 μM) forms but also prevented the parasite from infecting new host cells, reducing the infection rate by 3-fold compared to the untreated control. Similar results were obtained in L. infantum, with IC₅₀ = 2.5 and 1.0 μM for promastigote and amastigote forms, respectively. In active serum, GVL1-MAP2 continued to show high activity. GVL1-MAP2 also showed bactericidal activity against most strains tested. The bioconjugate GVL1-MAP2 showed lower cytotoxicity than GVL1-MAP1 and amphotericin B in macrophages. Permeabilization studies and enzyme inhibition revealed that the peptide acts via at least two distinct mechanisms, with the primary mechanism targeting the membrane and inner targets as an inhibitor of the CPB enzyme. Conclusions: These data demonstrated that the synthesis of bioconjugates can be a tool for the development of bactericidal and antileishmanial compounds with improved potency and selectivity.