Interfacing aptamers, nanoparticles and graphene in a hierarchical structure for highly selective detection of biomolecules in OECT devices

In several biomedical applications, the detection of biomarkers demands high sensitivity, selectivity and easy-to-use devices. Organic electrochemical transistors (OECTs) represent a promising class of devices combining a minimal invasiveness and good signal transduction. However, OECTs lack of intrinsic selectivity that should be implemented by specific approaches to make them well suitable for biomedical applications. Here, we report on a biosensor in which selectivity and a high sensitivity are achieved by interfacing, in an OECT architecture, a novel gate electrode based on aptamers, Au nanoparticles and graphene hierarchically organized to optimize the final response. The fabricated biosensor performs state of the art limit of detection monitoring biomolecules, such as thrombin-with a limit of detection in the picomolar range (≤ 5 pM) and a very good selectivity even in presence of supraphysiological concentrations of Bovine Serum Albumin (BSA-1mM). These accomplishments are the final result of the gate hierarchic structure that reduces sterich indrance that could contrast the recognition events and minimizes false positive, because of the low affinity of graphene towards the physiological environment. Since our approach can be easily applied to a large variety of different biomarkers, we envisage a relevant potential for a large series of different biomedical applications

Pollen-based natural nanostructures to realize nanoplasmonic biochips for single-molecule detection

In this work, a paradigm change in the development of the plasmonic-based bio/chemical sensing approaches is presented. The proposed idea is to use natural nanostructures instead of those fabricated by electron-beam lithography (EBL) tools. This sensing approach produces several advantages, such as high performances without an optimization step and a simple, low-cost, and eco-friendly production process with respect to other methods, which are still time-consuming with low scalability. In particular, pollen's nanostructures covered by gold nanofilms are used to realize gold nanogratings (GNG), similar to those made via EBL, to excite hybrid plasmonic phenomena. Bulk and binding sensitivities are evaluated and compared to nanoplasmonic sensors, particularly those achieved via an EBL-based chip. As proof of principle, an estrogen receptor (ERα) is immobilized on the plasmonic nanostructured surfaces of both EBL-based and pollen-based chips and interrogated by the same custom 3D-printed holder through a transmission-based experimental setup, exploiting polymer optical fibers (POFs). The experimental results demonstrate that the proposed pollen-based nanoplasmonic biosensor shows performance very similar to an EBL-based nanoplasmonic biosensor, indicating the equivalence between the two nanoplasmonic biosensors. The biosensor exhibited a detection limit better than 1 aM for the estradiol, demonstrating the capabilities of the proposed sensing approach towards single-molecule detection

A Review of Apta-POF-Sensors: The Successful Coupling between Aptamers and Plastic Optical Fibers for Biosensing Applications

Aptamers represent the next frontier as biorecognition elements in biosensors thanks to a smaller size and lower molecular weight with respect to antibodies, more structural flexibility with the possibility to be regenerated, reduced batch-to-batch variation, and a potentially lower cost. Their high specificity and small size are particularly interesting for their application in optical biosensors since the perturbation of the evanescent field are low. Apart from the conventional plasmonic optical sensors, platforms based on silica and plastic optical fibers represent an interesting class of devices for point-of-care testing (POCT) in different applications. The first example of the coupling between aptamers and silica optical fibers was reported by Pollet in 2009 for the detection of IgE molecules. Six years later, the first example was published using a plastic optical fiber (POF) for the detection of Vascular Endothelial Growth Factor (VEGF). The excellent flexibility, great numerical aperture, and the large diameter make POFs extremely promising to be coupled to aptamers for the development of a sensitive platform easily integrable in portable, small-size, and simple devices. Starting from silica fiber-based surface plasmon resonance devices, here, a focus on significant biological applications based on aptamers, combined with plasmonic-POF probes, is reported

Covalently Anchored Lipid Structures on Amine-Enriched Polystyrene

The study of the adhesion of lipid vesicles on surfaces is of increasing interest in the field of medical implants and tissue engineering (protein-resistant surfaces), drug delivery, biosensors, and biochips. In this work, lipid coverage was developed from PEG-coated vesicles (with sizes from 100 to 300 nm) by covalently binding poly(ethylene glycol)-alpha-disteroylphosphatidylethanolamine-omega-benzotriazole carbonate (DSPE-PEG-BTC) molecules onto the surface amine groups by carbamate chemistry. Lipid surface density and the surface structure of multilamellar (MLVs) and extruded unilamellar (LUVs) vesicles deposited on three types of polystyrene (PS) well-plates were probed by fluorescence and atomic force microscopy (AFM) imaging. A significant difference in the vesicle surface coverage of PS substrates was observed with a substantial increase in lipid multilayers on the amine-enriched PS surface using both unilamellar and multilamellar vesicles

Innovative microRNA purification based on surface properties modulation

The increasing interest in circulating microRNAs (miRNAs) as potential non-invasive cancer biomarkers has prompted the rapid development of several extraction techniques. However, current methods lack standardization and are costly and labor intensive. In light of this, we developed a microRNA solid-phase extraction strategy based on charge and roughness modulation on substrate surfaces. PECVD treated silicon oxide (PECVD-SO) and thermally grown silicon oxide (TG-SO) surfaces were functionalized with positively charged 3-aminopropyltriethoxysilanes (APTES) and neutral poly(ethylene glycol) silanes (PEG-s) mixed in different proportions to modulate the density of net positive charges and the roughness of the substrate. Characterization of the surfaces was performed by atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS) and s-SDTB (sulfosuccinimidyl-4-o-(4,4-dimethoxytrityl) butyrate) assay in order to investigate the surface morphology and chemical composition, respectively. Adsorption and elution efficiency were assessed by fluorescence microscopy by means of synthetic fluorescently labeled microRNAs. We identified PECVD-SO functionalized with 0.1% APTES and 0.9% 21–24 units long PEG-s as a promising surface able to selectively bind microRNAs and release them in the presence of a basic buffer (pH = 9) compatible with downstream analyses. MicroRNA integrity was assessed by reverse transcription and real-time PCR and confirmed by electrophoresis (Agilent 2100 Bioanalyzer), while binding competition from circulating DNA and proteins was excluded by fluorescence analyses and real-time PCR. On the contrary, total RNA slightly decreased miRNA adsorption. In conclusion, we showed an innovative and easy solid-state purification method for circulating miRNAs based on charge interaction, which could pave the path to future diagnostic and prognostic assays feasible as a routine test

A multimode plastic optical fiber platform coupled with aptamer layer for cancer biomarkers detection

Protein biomarkers are increasingly becoming significant analytical tools in the clinical practice. The introduction of new compact systems for sensitive, fast and simplified analysis is currently playing a substantial role in the development of point-of-care solutions driven by diagnostic and prognostic aims. The developed system represents a compact and miniaturized Lab-On-A-Chip (LOC) microdevice addressing the requirement of a rapid, portable, compact and low cost diagnostic platforms. For low-cost sensing systems, POFs are indeed especially advantageous due to their excellent flexibility, easy manipulation, great numerical aperture, large diameter, and thanks to the fact that plastic is able to withstand smaller bend radii than glass