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In the current study, we describe a novel, simple, inexpensive, sensitive, specific, stable and label-free electrochemical DNA biosensor used to identify a target gene cloned into a plasmid. The biosensor was designed with a 23-mer oligonucleotide of guanine-free, which was immobilized on the pencil graphite electrode (PGE) for E6 gene detection from human papillomavirus 16 type (HPV16). The E6 gene was used due to its clinical importance. The optimal probe concentration was obtained in 500 nM. The hybridization detection showed a good linearity in the range of 40–5,000 pg/μL with a detection limit of 16 pg/μL. The electrochemical method showed higher sensitivity and specificity when compared with the agarose gel electrophoresis assay. This technology could be postulated as a new and attractive alternative for cloning analysis in plasmids.

Dengue fever is the most prevalent vector-borne disease in the world, with nearly 100 million people infected every year. Early diagnosis and identification of the pathogen are crucial steps for the treatment and for prevention of the disease, mainly in areas where the co-circulation of different serotypes is common, increasing the outcome of dengue hemorrhagic fever (DHF) and dengue shock syndrome (DSS). Due to the lack of fast and inexpensive methods available for the identification of dengue serotypes, herein we report the development of an electrochemical DNA biosensor for the detection of sequences of dengue virus serotype 3 (DENV-3). DENV-3 probe was designed using bioinformatics software and differential pulse voltammetry (DPV) was used for electrochemical analysis. The results showed that a 22-m sequence was the best DNA probe for the identification of DENV-3. The optimum concentration of the DNA probe immobilized onto the electrode surface is 500 nM and a low detection limit of the system (3.09 nM). Moreover, this system allows selective detection of DENV-3 sequences in buffer and human serum solutions. Therefore, the application of DNA biosensors for diagnostics at the molecular level may contribute to future advances in the implementation of specific, effective and rapid detection methods for the diagnosis dengue viruses.

The detection and identification of human body fluids at crime scenes is usually performed using colorimetric and crystallographic tests. However, these assays may limit the samples detection during the washing steps. Currently, biosensors are emerging as alternative devices in molecular biology, combining the specificity and sensitivity of biological systems with the computing power of microprocessors. Herein, we report a preliminary study of an electrochemical biosensor able to detect DNA sequences in solutions mixed with household cleaners, aiming to simulate the effects of these chemicals on sample detection. The device was made using pencil graphite, acting as a working electrode (PGE) and an Ag/AgCl pin as a reference electrode. Single-strand DNA probes (ssDNA) were immobilized on PGE surface and the hybridization assay was performed by immersing the ssDNA–PGE electrode in a buffer solution with the target sequence under specific annealing temperature for 10min. Samples contamination was stimulated by household cleaners by immersing dsDNA–PGE immersed in solutions containing sodium hypochlorite, alcohol and SDS for 30min. The current peaks obtained with ssDNA–PGE and dsDNA–PGE were highly distinguishable (118.6nA and 24.435nA, respectively), even when dsDNA–PGE was mixed with sodium hypochloride, alcohol and detergent (17.12nA, 35.81nA and 69.44nA, respectively). These findings suggest that DNA biosensors have a great potential to be used as a confirmatory test to detect human body fluids in crime scenes.

An electrochemical DNA biosensor for human papillomavirus (HPV) 16 detection has been developed. For this proposed biosensor, L-cysteine was first electrodeposited on the gold electrode surface to form L-cysteine film (CYSFILM). Subsequently, HPV16-specific probe was immobilized on the electrode surface with CYSFILM. Electrochemistry measurement was studied by differential pulse voltammetry method (DPV). The measurement was based on the reduction signals of methylene blue (MB) before and after hybridization either between probe and synthetic target or extracted DNA from clinical samples. The effect of probe concentration was analyzed and the best results were seen at 1000 nM. The hybridization detection presented high sensitivity and broad linear response to the synthetic-target concentration comprised between 18.75 nM and 250 nM as well as to a detection limit of 18.13 nM. The performance of this biosensor was also investigated by checking probe-modified electrode hybridization with extracted DNA from samples. The results showed that the biosensor was successfully developed and exhibited high sensitivity and satisfactory selectivity to HPV16. These results allow for the possibility of developing a new portable detection system for HPVs and for providing help in making an effective diagnosis in the early stages of infection.