A highly reusable genosensor for late-life depression diagnosis based on microRNA 184 attomolar detection in human plasma.

Late-Life Depression (LLD) is one of the most prevalent psychiatric disorders in elderly, causing significant functional impairments. MicroRNAs are small molecules involved in the post-transcriptional regulation of gene expression. Elderly individuals diagnosed with LLD present down regulation of miR-184 (hsa-miR-184) expression compared to healthy patients. Therefore, this miR-184 can be used as a biomarker to diagnose LLD. Current LLD diagnosis depends primarily on clinical subjective identification, based on symptoms and variable scales. This work introduces a novel and facile approach for the LLD diagnosis based on the development of an electrochemical genosensor for miR-184 detection in plasma, using differential pulse voltammetry (DPV) and electrochemical impedance spectroscopy (EIS). DPV results presented a 2-Fold increase in current value for healthy patients, compared to individuals with LLD when monitoring ethidium bromide oxidation peak. For EIS, a 1.5-fold increase in charge transfer resistance for healthy elderly subjects was observed in comparison with depressed patients. In addition, the analytical performance of the biosensor was evaluated using DPV, obtaining a linear response ranging from 10-9 mol L-1 to 10-17 mol L-1 of miR-184 in plasma and a detection limit of 10 atomoles L-1. The biosensor presented reusability, selectivity and stability, the current response remained 72% up to 50 days of storage. Thus, the genosensor proved to be efficient in the diagnosis of LLD, as well as the accurate quantification of miR-184 in real plasma samples of healthy and depressed patients.

Electro-immunosensor for ultra-sensitive determination of cardiac troponin I based on reduced graphene oxide and polytyramine.

This work reports the construction of a novel nanostructured immunosensor for detection of the troponin I biomarker (cTnI). Anti-troponin I antibody was anchored on the modified graphite electrode with reduced graphene oxide and polytyramine for detection of troponin I in serum samples. The performance of the electro-immunosensor was evaluated by differential pulse voltammetry. The immunosensor presented a wide work range, from 4 ng mL-1 to 4 pg mL-1 , whose detection limit (4 pg mL-1 ) is significantly lower than the basal level in human serum, and maintained 100% of response after 30 days of storage. Moreover, the immunosensor showed good selectivity for detection of cTnI in real sample containing interfering substances and specificity of response to cTnI in the serum of healthy and sick patients, and demonstrated the possibility of reuse for two consecutive analyses, in addition to using a simplified and inexpensive platform when compared to other devices, demonstrating them excellent potential for application in diagnosis in the early stages of acute myocardial infarction.

Ninhydrin as a novel DNA hybridization indicator applied to a highly reusable electrochemical genosensor for Candida auris.

This work reports a simple strategy for Candida auris genomic DNA (gDNA) detection, a multi-resistant fungus associated with nosocomial outbreaks in healthcare settings, presenting high mortality and morbidity rates. The platform was developed using gold electrode sensitized with specific DNA capture probe and ninhydrin as a novel DNA hybridization indicator. The genosensor was able to detect C. auris in urine sample by differential pulse voltammetry and electrochemical impedance spectroscopy. The biosensor's analytical performance was evaluated by differential pulse voltammetry, detecting up to 4.5 pg µL-1 of C. auris gDNA in urine (1:10, V/V). Moreover, the genosensor was reused eight times with no loss in the current signal response. The genosensor showed selectivity and stability, maintaining 100% of its response up to 80 days of storage. In order to analyze interactions of single and double-stranded DNA with ninhydrin, SEM, AFM and molecular dynamics studies followed by docking simulations were performed. Theoretical calculations showed ninhydrin interactions more favorably with dsDNA in an A-T rich binding pocket rather than with the ssDNA. Therefore, the proposed system is a promising electrochemical detection device towards a more accurate detection of C. auris gDNA in biological samples.

A novel peptide-based sensor platform for detection of anti-Toxoplasma gondii immunoglobulins.

Toxoplasma gondii is an intracellular protozoan parasite responsible for toxoplasmosis, which affects humans and animals. Serologic detection of anti-T. gondii immunoglobulins plays a crucial role in the clinical diagnosis of toxoplasmosis. In this work, a novel electrochemical immunosensor for detecting anti-T. gondii immunoglobulins is reported, based on immobilization of an in silico predicted peptide (PepB3), obtained from membrane protein of T. gondii, on the graphite electrode modified with poly(3-hydroxybenzoic acid). Indirect ELISA confirmed infection and binding specificity of peptide PepB3. Molecular modelling and simulations show this peptide binds to the T. gondii human Fab antibody in the surface antigen 1 (SAG1) binding site, remaining a stable complex during the molecular dynamic simulations, especially by hydrogen bonds and hydrophobic interactions. This electrochemical immunosensor was able to discriminate different periods of infection, using infected mouse serum samples, showing selectivity and discriminating infected and uninfected mouse serum.