A bioorganometallic approach for rapid electrochemical analysis of human immunodeficiency virus type-1 reverse transcriptase in serum

Application of the Curtius rearrangement to the synthesis of 1′-aminoferrocene-1-carboxylic acid derivatives

The shortest synthesis of N-protected 1′-aminoferrocene-1-carboxylic acid from readily available ferrocene-1,1′-dicarboxylic acid is reported.

Protein electrocatalysis for direct sensing of circulating microRNAs

MicroRNAs (miRNAs) are potentially useful biomarkers for diagnosis, classification, and prognosis of many diseases, including cancer. Herein, we developed a protein-facilitated electrocatalytic quadroprobe sensor (Sens(PEQ)) for detection of miRNA signature of chronic lymphocytic leukemia (CLL) in human serum. The developed signal-ON sensor provides a compatible combination of two DNA adaptor strands modified with four methylene blue molecules and electrocatalysis using glucose oxidase in order to enhance the overall signal gain. This enhanced sensitivity provided the response necessary to detect the low-abundant serum miRNAs without preamplification. The developed Sens(PEQ) is exquisitely sensitive to subtle π-stack perturbations and capable of distinguishing single base mismatches in the target miRNA. Furthermore, the developed sensor was employed for profiling of three endogenous miRNAs characteristic to CLL, including hsa-miR-16-5p, hsa-miR-21-5p, and hsa-miR-150-5p in normal healthy serum, chronic lymphocytic leukemia Rai stage 1 (CLL-1), and stage 3 (CLL-3) sera, using a non-human cel-miR-39-3p as an internal standard. The sensor results were verified by conventional SYBR green-based quantitative reverse-transcription polymerase chain reaction (RT-qPCR) analysis.

Electrochemical sensing of microRNAs: avenues and paradigms

Twenty years has passed since the first discovery of microRNA (miRNA) lin-4 in Caenorhabditis elegans. Over the last two decades, the study of miRNAs has attracted tremendous attention. These new stars of biomarkers are naturally occurring non-coding RNAs that regulate gene expression posttranscriptionally and have been demonstrated to be dysregulated in many diseases. Since their profiles reflect pathological conditions, miRNAs have recently been proposed as biomarkers of the onset, prognosis and risk of diseases, as well as in the classification of different types of cancer. The establishment of miRNA profiles for diseases and the detection of different types and levels of miRNAs in biological samples are therefore critical milestones in diagnostics. This provides powerful impetus and a growing demand for researchers to develop simple analytical techniques to allow for an accurate, sensitive, selective, and cost effective miRNA analysis at point-of-care settings. Among several methods proposed for miRNA detection, electrochemical nucleic acid biosensors exhibit many attractive features and could play a leading role in future miRNA detection and quantification. This review gives an overview of recent advances in the rapidly growing area of electrochemical detection of miRNAs. The fundamentals of the different strategies adopted for miRNA detection are discussed and some examples of relevant approaches are highlighted, along with future prospects and challenges.

Three-mode electrochemical sensing of ultralow microRNA levels

MicroRNAs (miRNAs) are an emerging class of biomarkers that are frequently deregulated in cancer cells and have shown great promise for cancer classification and prognosis. In this work, we developed a three-mode electrochemical sensor for detection and quantitation of ultralow levels of miRNAs in a wide dynamic range of measured concentrations. The sensor facilitates three detection modalities based on hybridization (H-SENS), p19 protein binding (P-SENS), and protein displacement (D-SENS). The combined three-mode sensor (HPD-SENS) identifies as low as 5 aM or 90 molecules of miRNA per 30 μL of sample without PCR amplification, and can be operated within the dynamic range from 10 aM to 1 μM. The HPD sensor is made on a commercially available gold nanoparticles-modified electrode and is suitable for analyzing multiple miRNAs on a single electrode. This three-mode sensor exhibits high selectivity and specificity and was used for sequential analysis of miR-32 and miR-122 on one electrode. In addition, the H-SENS can recognize miRNAs with different A/U and G/C content and distinguish between a fully matched miRNA and a miRNA comprising either a terminal or a middle single base mutation. Furthermore, the H- and P-SENS were successfully employed for direct detection and profiling of three endogenous miRNAs, including hsa-miR-21, hsa-miR-32, and hsa-miR-122 in human serum, and the sensor results were validated by qPCR.

Multifunctional electrochemical aptasensor for aptamer clones screening, virus quantitation in blood and viability assessment

A novel attempt was made to develop a disposable multifunctional sensor for analysis of vaccinia virus (VACV), a promising oncolytic agent that can replicate in and kill tumor cells. Briefly, we developed aptamers specific to VACV that were negatively selected against human serum as well as human and mouse blood to be further utilized for viral analysis directly in serum and blood. In addition, the aptamers were negatively selected against heat-inactivated VACV to enable them to distinguish between viable and nonviable virus particles. The selected aptamers were integrated onto an electrochemical aptasensor to perform multiple functions, including quantification of VACV, viability assessment of the virus, and estimation of the binding affinity between the virus and the developed aptamers. The aptasensor was fabricated by self-assembling a hybrid of a thiolated ssDNA primer and a VACV-specific aptamer onto a gold nanoparticles modified screen-printed carbon electrode (GNPs-SPCE). Square wave voltammetry was employed to quantify VACV in serum and blood within the range of 150-900 PFU, with a detection limit of 60 PFU in 30 μL. According to the electrochemical affinity measurements, three virus specific aptamer clones, V-2, V-5, and V-9 exhibited the highest affinity to VACV. Furthermore, flow cytometry was employed to estimate the dissociation constants of the clones which were found to be 26.3, 40.9, and 24.7 nM, respectively. Finally, the developed aptasensor was able to distinguish between the intact virus and the heat-inactivated virus thanks to the tailored selectivity of the aptamers that was achieved via negative selection.

Electrochemical aptasensors for microbial and viral pathogens

Aptamers are DNA and RNA oligonucleotides that can bind to a variety of nonnucleic acid targets with high affinity and specificity. Pathogen detection is a promising area in aptamer research. One of its major advantages is the ability of the aptamers to target and specifically differentiate microbial and viral strains without previous knowledge of the membrane-associated antigenic determinants or molecular biomarkers present in that particular microorganism. Electrochemical sensors emerged as a promising field in the area of aptamer research and pathogen detection. An electrochemical sensor is a device that combines a recognition element and an electrochemical transduction unit, where aptamers represent the latest addition to the large catalog of recognition elements. This chapter summarizes and evaluates recent developments of electrochemical aptamer-based sensors for microbial and viral pathogen detection, viability assessment of microorganisms, bacterial typing, identification of epitope-specific aptamers, affinity measurement between aptamers and their respective targets, and estimation of the degree of aptamer protection of oncolytic viruses for therapeutic purposes.

Electrochemical differentiation of epitope-specific aptamers

DNA aptamers are promising immunoshielding agents that could protect oncolytic viruses (OVs) from neutralizing antibodies (nAbs) and increase the efficiency of cancer treatment. In the present Article, we introduce a novel technology for electrochemical differentiation of epitope-specific aptamers (eDEA) without selecting aptamers against individual antigenic determinants. For this purpose, we selected DNA aptamers that can bind noncovalently to an intact oncolytic virus, vaccinia virus (VACV), which can selectively replicate in and kill only tumor cells. The aptamers were integrated as a recognition element into a multifunctional electrochemical aptasensor. The developed aptasensor was used for the linear quantification of the virus in the range of 500-3000 virus particles with a detection limit of 330 virions. Also, the aptasensor was employed to compare the binding affinities of aptamers to VACV and to estimate the degree of protection of VACV using the anti-L1R neutralizing antibody in a displacement assay fashion. Three anti-VACV aptamer clones, vac2, vac4, and vac6, showed the best immunoprotection results and can be applied for enhanced delivery of VACV. Another two sequences, vac5 and vac46, exhibited high affinities to VACV without shielding it from nAb and can be further utilized in sandwich bioassays.

A novel biosensor based on serum antibody immobilization for rapid detection of viral antigens

In this paper, we represent a label-free biosensor based on immobilization of serum antibodies for rapid detection of viral antigens. Human serum containing specific antibodies against Japanese encephalitis virus (JEV) was immobilized on a silanized surface of an interdigitated sensor via protein A/glutaraldehyde for electrical detection of JEV antigens. The effective immobilization of serum antibodies on the sensor surface was verified by Fourier transform infrared spectrometry and fluorescence microscopy. The signal of the biosensor obtained by the differential voltage converted from the change into non-Faradic impedance resulting from the specific binding of JEV antigens on the surface of the sensor. The detection analyzed indicates that the detection range of this biosensor is 1-10 μg/ml JEV antigens, with a detection limit of 0.75 μg/ml and that stable signals are measured in about 20 min. This study presents a useful biosensor with a high selectivity for rapid and simple detection of JEV antigens, and it also proposes the biosensor as a future diagnostic tool for rapid and direct detection of viral antigens in clinical samples for preliminary pathogenic screenings in the case of possible outbreaks.