Capacitive spectroscopy as transduction mechanism for wearable biosensors: opportunities and challenges.

Wearable sensors would revolutionize healthcare and personalized medicine by providing individuals with continuous and real-time data about their bodies and environments. Their integration into everyday life has the potential to enhance well-being, improve healthcare outcomes, and offer new opportunities for research. Capacitive sensors technology has great potential to enrich wearable devices, extending their use to more accurate physiological indicators. On the basis of capacitive sensors developed so far to monitor physical parameters, and taking into account the advances in capacitive biosensors, this work discusses the benefits of this type of transduction to design wearables for the monitoring of biomolecules. Moreover, it provides insights into the challenges that must be overcome to take advantage of capacitive transduction in wearable sensors for health.

Enzyme-Linked DNA Displacement (ELIDIS) Assay for Ultrasensitive Electrochemical Detection of Antibodies.

Here we report the development of a method for the electrochemical ultrasensitive detection of antibodies that couples the programmability and versatility of DNA-based systems with the sensitivity provided by enzymatic amplification. The platform, termed Enzyme-Linked DNA Displacement (ELIDIS), is based on the use of antigen-DNA conjugates that, upon the bivalent binding of a specific target antibody, induce the release of an enzyme-DNA hybrid strand from a preformed duplex. Such enzyme-DNA hybrid strand can then be electrochemically detected with a disposable electrode with high sensitivity. We applied ELIDIS to demonstrate the sensitive (limit of detection in the picomolar range), specific and multiplexed detection of five different antibodies including three clinically relevant ones. ELIDIS is also rapid (it only requires two reaction steps), works well in complex media (serum) and is cost-effective. A direct comparison with a commercial ELISA kit for the detection of Cetuximab demonstrates the promising features of ELIDIS as a point-of-care platform for antibodies detection.

Electrochemical Cellulase-Linked ELASA for Rapid Liquid Biopsy Testing of Serum HER-2/neu.

Non-invasive liquid biopsy assays for blood-circulating biomarkers of cancer allow both its early diagnosis and treatment monitoring. Here, we assessed serum levels of protein HER-2/neu, overexpressed in a number of aggressive cancers, by the cellulase-linked sandwich bioassay on magnetic beads. Instead of traditional antibodies we used inexpensive reporter and capture aptamer sequences, transforming the enzyme-linked immuno-sorbent assay (ELISA) into an enzyme-linked aptamer-sorbent assay (ELASA). The reporter aptamer was conjugated to cellulase, whose digestion of nitrocellulose film electrodes resulted in the electrochemical signal change. ELASA, optimized relative aptamer lengths (dimer vs monomer and trimer), and assay steps allowed 0.1 fM detection of HER-2/neu in the 10% human serum in 1.3 h. Urokinase plasminogen activator and thrombin as well as human serum albumin did not interfere, and liquid biopsy analysis of serum HER-2/neu was similarly robust but 4 times faster and 300 times cheaper than both electrochemical and optical ELISA. Simplicity and low cost of cellulase-linked ELASA makes it a perspective diagnostic tool for fast and accurate liquid biopsy detection of HER-2/neu and of other proteins for which aptamers are available.

Electrochemical ELASA: improving early cancer detection and monitoring.

The discovery of new molecular biomarkers of cancer during the last decades and the development of new diagnostic devices exploiting those have significantly contributed to the clinical analysis of cancer and to improve the outcomes. Among those, liquid biopsy sensors exploiting aptamers for the detection of cancer biomarkers in body fluids are useful and accurate tools for a fast and inexpensive non-invasive screening of population. The incorporation of aptamers in electrochemical sandwich biosensors using enzyme labels, a so-called ELASA, has demonstrated its utility to improve the detection schemes. In this review, we overview the existing ELASA assays for numerous cancer biomarkers as alternatives to the traditional ELISA and discuss their possibilities to reach the market, currently dominated by optical immunoassays.

Covalent Hemin/G4 complex-linked sandwich bioassay on magnetic beads for femtomolar HER-2/neu detection in human serum via direct electrocatalytic reduction of oxygen.

Liquid biopsy assays for tumour biomarkers circulating in blood are perspective non-invasive tools for cancer diagnosis and treatment monitoring. Here, we suggest a simple, 1 h long electrochemical DNAzyme-linked aptamer- and immuno-sandwich magnetic assay for analysis of serum HER-2/neu protein overexpressed in several aggressive cancers. In the assay, we used a covalent hemin-guanine quadruplex (G4) complex as a novel O2-dependent electrocatalytic label that allowed 10 fM (aptamer-aptamer) and 1 fM (aptamer-antibody) detection of HER-2/neu in human serum. The O2 reactivity of the aptamer-conjugated label was detected at high-surface-area graphite electrodes displaying a high efficiency of O2 reduction electro-catalyzed by this DNAzyme. In contrast to the recognised H2O2 reactivity, the O2 reactivity of the covalent hemin/G4 complex depended only on ambient O2 present in solutions, and did not require adding such traditional reagents as hemin and H2O2, and solution de-aeration. Human serum albumin, urokinase plasminogen activator and thrombin did not interfere, and the assay was used for analysis of basal serum levels of HER-2/neu. Due to the simplicity and low cost, sandwich assays exploiting O2-linked electrocatalysis by the covalent hemin-G4 complexes represent a more advanced electrochemical ELISA platform for ultrasensitive and fast detection of low concentrations of proteins in complex biological matrices.

Ultrasensitive disposable apatasensor for reagentless electrocatalytic detection of thrombin: An O2-Dependent hemin-G4-aptamer assay on gold screen-printed electrodes.

Serine protease thrombin is a strong neurotoxin produced by the injured brain and an Alzheimer's disease biomarker. To address its point-of-care testing (POCT), we adapted the O2-dependent aptamer assay for thrombin to gold screen-printed electrodes (Au SPE). The assay exploits reagentless (with no mediators) electrocatalytic activity of hemin-G4 DNAzyme in O2 reduction. Au SPEs modified with thiolated hemin-conjugated aptamer and PEG showed enhanced electrocatalytic activity in O2 reduction upon thrombin binding to the aptamer, then folding into the electroactive hemin-G4 DNAzyme structure. 0.5 fM thrombin were detected in aerated PBS and artificial cerebrospinal fluid, correspondingly, with the logarithmic linear range extending to 100 fM; dopamine, and uric and ascorbic acids did not interfere with electroanalysis. The disposable aptasensor met basic POCT requirements, with a minimal shelf life of 3 days. However, the reactivity and suitability of the Au SPE surface for thiol binding and electrocatalysis required special surface pre-treatment and modification protocols, and the fundamental problem of a long-term stability of thiol modification on gold should be addressed for practical applications of Au SPE-based apatasensors in POCT.

Impedimetric aptamer-based glycan PSA score for discrimination of prostate cancer from other prostate diseases.

Prostate specific antigen (PSA) is the common biomarker for prostate cancer (PCa). However, its lack of specificity to differentiate PCa from benign prostate disorders stimulates the search for alternative cancer biomarkers to improve the clinical management of the patients. Different studies have described changes in the core-fucosylation level of PSA between PCa patients and healthy controls. To exploit these findings, we have adapted an impedimetric aptamer-based sensor to the dual recognition of PSA. Two different aptamers, PSAG-1 and anti-PSA, are immobilized onto two adjacent nanostructured gold electrodes. The direct binding from diluted serum samples of specific glycosylated-PSA to the first sensor and total PSA to the second one leads to changes in the charge transfer resistance, which correlate to the amount of glycosylated and total PSA in the sample. The sensors are able to measure PSA in serum with a dynamic range between 0.26 and 62.5 ng/mL (PSAG-1) and from 0.64 to 62.5 ng/mL (anti-PSA), with a reproducibility of 5.4 %. The final output of the proposed platform is the ratio between PSAG-1 reactive PSA and total PSA, defined as the glycan score. The glycan score was tested in serum samples from patients with different pathologies, showing excellent correlation between the measured score and the known diagnosis of the patients. Hence this dual aptamer-based impedimetric biosensor could be used as a minimally invasive method for the diagnosis of prostate cancer.

Electrochemical aptasensors for cancer diagnosis in biological fluids - A review.

The tunability of SELEX procedure is an essential feature to supply bioaffinity receptors (aptamers) almost on demand for analytical and therapeutic purposes. This longstanding ambition is, however, not straightforward. Non-invasive cancer diagnosis, so called liquid biopsy, requires collection of body fluids with minimal or no sample pretreatment. In those raw matrices, aptamers must recognize minute amounts of biomarkers that are not unique entities but large sets of variants evolving with the disease stage. The susceptibility of aptasensors to assay conditions has driven the selection of aptamers to natural environments to ensure their optimum performance in clinical samples. We present herein a compilation of the SELEX procedures in natural milieus. By revising the electrochemical aptasensors applied to clinical samples for cancer diagnosis and tracing back to the original SELEX we analyze whether aptamers raised using these SELEX strategies are being incorporated to the diagnostic devices and how aptasensors are finding their way to a market dominated by antibody-based assays.

Aptamers targeting protein-specific glycosylation in tumor biomarkers: general selection, characterization and structural modeling.

Detecting specific protein glycoforms is attracting particular attention due to its potential to improve the performance of current cancer biomarkers. Although natural receptors such as lectins and antibodies have served as powerful tools for the detection of protein-bound glycans, the development of effective receptors able to integrate in the recognition both the glycan and peptide moieties is still challenging. Here we report a method for selecting aptamers toward the glycosylation site of a protein. It allows identification of an aptamer that binds with nM affinity to prostate-specific antigen, discriminating it from proteins with a similar glycosylation pattern. We also computationally predict the structure of the selected aptamer and characterize its complex with the glycoprotein by docking and molecular dynamics calculations, further supporting the binary recognition event. This study opens a new route for the identification of aptamers for the binary recognition of glycoproteins, useful for diagnostic and therapeutic applications.

Focusing aptamer selection on the glycan structure of prostate-specific antigen: Toward more specific detection of prostate cancer.

The development of chemical sensors capable of detecting the specific glycosylation patterns of proteins offers a powerful mean for the early detection of cancer. Unfortunately, this strategy is scarcely explored because receptors recognizing the glycans linked to proteins are challenging to discover. In this work, we describe a simple method for directing the selection of aptamers toward the glycan structure of the glycoproteins, with prostate-specific antigen (PSA) as a model target. Using this strategy, we identified one aptamer (PSA-1) that binds the glycan moiety of PSA with reasonable affinity (a dissociation constant of 177 ±â€¯65 nM). Interestingly, an electrochemical sensor with a sandwich format employing the identified aptamer as a signaling receptor, provides a tool of discriminating human PSA from the unglycosylated protein, with a limit of detection of 0.66 ng/mL. The sensor responds to different levels of PSA in serum, correlating well with chemiluminescence ELISA used in hospitals even with higher potential to discriminate clinically meaningful prostate cancer. Although validation on a larger cohort is needed, this is the first demonstration of an aptamer-based sensor to detect PSA by focusing in its glycan moiety.

Post-translational modifications in tumor biomarkers: the next challenge for aptamers?

Advances in proteomics have fueled the search for novel cancer biomarkers with higher selectivity. Differential expression of low abundant proteins has been the usual way of finding those biomarkers. The existence of a selective receptor for each biomarker is compulsory for their use in diagnostic/prognostic assays. Antibodies are the receptors of choice in most cases although aptamers are becoming familiar because of their facile and reproducible synthesis, chemical stability as well as comparable affinity and selectivity. In recent years, it has been reported that the pattern of post-translational modifications, altered under neoplastic disease, is a better predictive biomarker than the total protein level. Among others, abnormal glycosylation is attracting great attention. Lectins and antibodies are being used for identification and detection of the carbohydrate moiety with low level of discrimination among various glycoproteins. Such level of selectivity is critical to bring next-generation biomarkers to the clinic. Aptamers that can be rationally tailored for a certain molecule domain can become the golden receptor to specifically detect aberrant glycosylation at each protein or even at each glycosylation site, providing new diagnostic tools for early detection of cancer. Graphical abstract Aptamers may specifically differentiate normal from aberrant glycoproteins.

Evaluación de la exposición a plaguicidas organofosforados y carbamatos según índice de colinesterasa sanguínea / Assessment of exposure to organophosphate and carbamate pesticides according to the blood cholinesterase index

La media de la actividad colinesterásica en sangre total se utilizò como indicador de exposición de los grupos de riesgo (niños, mujeres y ancianos) de una comunidad situada a 2 km de un plan arrocero que recibe fumigaciones aéreas de organofosforados y carbamatos, se comparan con los resultados obtenidos en estos grupos de población de otra comunidad no expuesta. La mayoría de los casos estudiados presentan valores normales, pero se evidencia una tendencia a menor actividad de la colinesterasa en la muestra estudiada de la comunidad vecina a la zona arrocera

Evaluación de la exposición a plaguicidas organofosforados y carbamatos según índice de colinesterasa sanguínea / Assessent of exposure to organophosphate and carbamate pesticides according to the blood cholinesterase index

La media de la actividad colinesterásica en sangre total se utilizò como indicador de exposición de los grupos de riesgo (niños, mujeres y ancianos) de una comunidad situada a 2 km de un plan arrocero que recibe fumigaciones aéreas de organofosforados y carbamatos, se comparan con los resultados obtenidos en estos grupos de población de otra comunidad no expuesta. La mayoría de los casos estudiados presentan valores normales, pero se evidencia una tendencia a menor actividad de la colinesterasa en la muestra estudiada de la comunidad vecina a la zona arrocera

Estudio inmunológico de población adulta no laboral en dos comunidades con diferentes grados de utilización de plaguicidas con fines agricolas / Immunological study on non-working adult population in two comunities with different levels of pesticides use in agriculture

Se llevó a cabo un estudio inmunológico en grupos de riesgo de población adulta no laboral, en 2 comunidades con diferentes grados de exposición, con el objetivo de conocer la influencia de los plaguicidas sobre la salud de la población adulta. Se determinaron los niveles de inmunoglobulinas G,A y M, así como la fracción C3c del complemento. Los valores promedio de la IgA mostraron diferencia significativa entre ambas localidades, no así el resto de las variables estudiadas cuyo comportamiento fue similar. Se compararon los valores promedio de las inmunoglobulinas de la población no laboral del Corojal con los de un grupo de trabajadores del arroz de esa misma comunidad

Estudio inmunológico de población adulta no laboral en dos comunidades con diferentes grados de utilización de plaguicidas con fines agricolas / Imunological study on non-working adult population in two comunities with different levels of pesticides use in agriculture

Se llevó a cabo un estudio inmunológico en grupos de riesgo de población adulta no laboral, en 2 comunidades con diferentes grados de exposición, con el objetivo de conocer la influencia de los plaguicidas sobre la salud de la población adulta. Se determinaron los niveles de inmunoglobulinas G,A y M, así como la fracción C3c del complemento. Los valores promedio de la IgA mostraron diferencia significativa entre ambas localidades, no así el resto de las variables estudiadas cuyo comportamiento fue similar. Se compararon los valores promedio de las inmunoglobulinas de la población no laboral del Corojal con los de un grupo de trabajadores del arroz de esa misma comunidad

Estudio inmunológico de niños residentes en una comunidad expuesta a la utilización intensiva de plaguicidas con fines agrícolas / Inmunological study of children living in a conmunity exposed to intensive utilization of pesticides for agricultural purposes

Para conocer la influencia de los plaguicidas sobre la salud de la población infantil, se realizó un estudio inmunológico en una muestra de uno y otro sexos, comprendidos entre 5 y 9 años de edad, en 2 comunidades con diferentes grados de exposición a estos compuestos. Se determinaron los niveles de inmunoglobulinas G, A y M, así como la fracción C3c del complemento. Los valores promedio de la IGA y de la IGM mostraron diferencia significativa entre ambas comunidades, mientras que el comportamiento de la fracción C3c del complemento fue similar entre ambas poblaciones

Estudio inmunológico de niños residentes en una comunidad expuesta a la utilización intensiva de plaguicidas con fines agrícolas / Inmunological study of children living in a conmunity exposed to intensive utilization of pesticides for agricultural purposes

Para conocer la influencia de los plaguicidas sobre la salud de la población infantil, se realizó un estudio inmunológico en una muestra de uno y otro sexos, comprendidos entre 5 y 9 años de edad, en 2 comunidades con diferentes grados de exposición a estos compuestos. Se determinaron los niveles de inmunoglobulinas G, A y M, así como la fracción C3c del complemento. Los valores promedio de la IGA y de la IGM mostraron diferencia significativa entre ambas comunidades, mientras que el comportamiento de la fracción C3c del complemento fue similar entre ambas poblaciones

Niveles de diclorodifeniltricloroetano (DDT) y sus metabolitos en leche materna en Villa Clara, 1983 / Levels of chlorophenothane (DDT) and its etabolites in mother's milk, Villa Clara, 1983

Se analizaron los niveles de diclorodifeniltricloroetano (DDT) y sus metabolitos en 62 muestras de leche materna procedentes de madres ingresadas en el Hospital Ginecoobstétrico "Mariana Grajales" de la ciudad de Santa Clara, provincia de Villa Clara. Se estudió la posible correlación de los resultados con la edad, zona de permanencia, hábito de fumar, número de partos y días posparto de las madres donantes. El 100 de las muestras tuvo presencia de residuos de DDT total, con una media de 0,118 p.p.m.

Niveles de DDT y sus metabolitos en leche materna en Cuba: 1982-1985 / DDT levels and metabolites in breast milk in Cuba: 1982-1985

A fin de conocer los niveles de DDT y sus metabolitos en leche materna como un índice de la contaminación ambiental por este plaguicida y su incidencia en el hombre, se analizaron 424 muestras procedentes de madres de 8 localidades correspondientes a 6 provincias de Cuba, durante los años 1982-1985. El valor de la mediana encontrada en este estudio fue de 94 ppb. La localidad con más alto índice de DDT en leche materna resultó ser Güines, en Provincia Habana; y los niveles más bajos se encontraron en Ciudad de la Habana y Santiago de Cuba