An ultrasensitive optical biosensor for microRNA-155 (miR-155) was developed to diagnose breast cancer at early stages. At first, the probe DNA covalently bind to the negatively charged gold nanoparticles (citrate-capped AuNPs). Then, the target miR-155 electrostatically adsorb onto the positively charged gold nanoparticles (polyethylenimine-capped AuNP) surface. Finally, by mixing citrate-capped AuNP/probe and polyethylenimine-capped AuNP/miR-155, hybridization occurs and the optical signal of the mixture give a measure to quantify the miR-155 content. The proposed biosensor is able to specify 3-base-pair mismatches and genomic DNA from target miR-155. The novelty of this biosensor is in its ability to trap the label-free target by its branched positively charged polyethylenimine. This method increases loading the target on the polyethylenimine-capped AuNPs’ surface. So, proposed sensor enables miR-155 detection at very low concentrations with the detection limit of 100 aM and a wide linear range from 100 aM to 100 fM.

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The expression levels of many genes change after treatment of human immunodeficiency virus (HIV)‐infected subjects by antiretroviral drugs. High‐throughput analysis of tremendous datasets led to the discovery of genes that are implicated in the treatment pathways. In this study, we performed a gene‐enrichment analysis after determining the differentially expressed genes (DEGs) between untreated HIV‐positive and HIV‐negative subjects and also between treated HIV‐positive subjects with antiretroviral therapy (ART; who receiving nucleoside reverse transcriptase inhibitor–based ART) and untreated HIV‐positive cases in the peripheral blood mononuclear cells (PBMCs), adipose, and muscle tissues. In sum, the genes that activate inflammatory, immune response, proliferation, metabolism, and viral involvement pathways have different expression patterns in the untreated HIV‐positive subjects and treated HIV‐positive cases. Moreover, the expression levels of the genes including ACLY, ALDH18A1, HADHA, and YARS in the PBMCs tissue and HBEGF, PKN3, DEGS2, and EDN3 in the fat tissue were found to be different in the HIV‐infected patients, which can be considered as new biomarkers for HIV infection.

Due to the limited time pass (less than 5 years) for developing CRISPR/Cas-based electrochemical detection platforms, this field is very new. The number of experimental studies is limited, and this field does not take a long developmental path yet. Therefore expansion of ideas is limited based on some pioneering research. However, this does not diminish the importance and potential of this field. There is vast potential in the field of CRISPR/Cas-based diagnostics; as the electrochemical detection systems proved their abilities in the past, merging these two categories will mark a bright future with applications in very diverse subjects. This chapter attempts to brighten the potential of applications in this field. Despite the limited number of researches in this field, the diverse application of CRISPR/Cas-based electrochemical biosensors are reviewed here, which implicitly confirms the potential of this field. Due to the analytical advantage of the electrochemical-based detection system, in comparison to the other methods, electrochemical CRISPR/Cas-based detection systems will significantly impact improving public health quality through developing sensitive, reliable, and affordable point of care diagnostic devices and tests.