Femtomolar detection of the heart failure biomarker NT-proBNP in artificial saliva using an immersible liquid-gated aptasensor with reduced graphene oxide

Measuring NT-proBNP biomarker is recommended for preliminary diagnostics of the heart failure. Recent studies suggest a possibility of early screening of biomarkers in saliva for non-invasive identification of cardiac diseases at the point-of-care. However, NT-proBNP concentrations in saliva can be thousand time lower than in blood plasma, going down to pg/mL level. To reach this level, we developed a label-free aptasensor based on a liquid-gated field effect transistor using a film of reduced graphene oxide monolayer (rGO-FET) with immobilized NT-proBNP specific aptamer. We found that, depending on ionic strength of tested solutions, there were different levels of correlation in responses of electrical parameters of the rGO-FET aptasensor, namely, the Dirac point shift and transconductance change. The correlation in response to NT-proBNP was high for 1.6 mM phosphate-buffered saline (PBS) and zero for 16 mM PBS in a wide range of analyte concentrations, varied from 1 fg/mL to 10 ng/mL. The effects of transconductance and Dirac point shift in PBS solutions of different concentrations are discussed. The biosensor exhibited a high sensitivity for both transconductance (2 uS/decade) and Dirac point shift (2.3 mV/decade) in diluted PBS with the linear range from 10 fg/mL to 1 pg/mL. The aptasensor performance has been also demonstrated in undiluted artificial saliva with the achieved limit of detection down to 41 fg/mL (~4.6 fM)

Graphene-Based Sensing Platform for On-Chip Ochratoxin A Detection

In this work, we report an on-chip aptasensor for ochratoxin A (OTA) toxin detection that is based on a graphene field-effect transistor (GFET). Graphene-based devices are fabricated via large-scale technology, allowing for upscaling the sensor fabrication and lowering the device cost. The sensor assembly was performed through covalent bonding of graphene’s surface with an aptamer specifically sensitive towards OTA. The results demonstrate fast (within 5 min) response to OTA exposure with a linear range of detection between 4 ng/mL and 10 pg/mL, with a detection limit of 4 pg/mL. The regeneration time constant of the sensor was found to be rather small, only 5.6 s, meaning fast sensor regeneration for multiple usages. The high reproducibility of the sensing response was demonstrated via using several recycling procedures as well as various GFETs. The applicability of the aptasensor to real samples was demonstrated for spiked red wine samples with recovery of about 105% for a 100 pM OTA concentration; the selectivity of the sensor was also confirmed via addition of another toxin, zearalenone. The developed platform opens the way for multiplex sensing of different toxins using an on-chip array of graphene sensors

Photo-Induced Doping in a Graphene Field-Effect Transistor with Inkjet-Printed Organic Semiconducting Molecules

In this work, we report a novel method of maskless doping of a graphene channel in a field-effect transistor configuration by local inkjet printing of organic semiconducting molecules. The graphene-based transistor was fabricated via large-scale technology, allowing for upscaling electronic device fabrication and lowering the device’s cost. The altering of the functionalization of graphene was performed through local inkjet printing of N,N′-Dihexyl-3,4,9,10-perylenedicarboximide (PDI-C6) semiconducting molecules’ ink. We demonstrated the high resolution (about 50 µm) and accurate printing of organic ink on bare chemical vapor deposited (CVD) graphene. PDI-C6 forms nanocrystals onto the graphene’s surface and transfers charges via π–π stacking to graphene. While the doping from organic molecules was compensated by oxygen molecules under normal conditions, we demonstrated the photoinduced current generation at the PDI-C6/graphene junction with ambient light, a 470 nm diode, and 532 nm laser sources. The local (in the scale of 1 µm) photoresponse of 0.5 A/W was demonstrated at a low laser power density. The methods we developed open the way for local functionalization of an on-chip array of graphene by inkjet printing of different semiconducting organic molecules for photonics and electronics

Two-Photon Polymerization of Albumin Hydrogel Nanowires Strengthened with Graphene Oxide

Multifunctional biomaterials can pave a way to novel types of micro- and nanoelectromechanical systems providing benefits in mimicking of biological functions in implantable, wearable structures. The production of biocomposites that hold both superior electrical and mechanical properties is still a challenging task. In this study, we aim to fabricate 3D printed hydrogel from a biocomposite of bovine serum albumin with graphene oxide (BSA@GO) using femtosecond laser processing. We have developed the method for functional BSA@GO composite nanostructuring based on both two-photon polymerization of nanofilaments and direct laser writing. The atomic-force microscopy was used to probe local electrical and mechanical properties of hydrogel BSA@GO nanowires. The improved local mechanical properties demonstrate synergistic effect in interaction of femtosecond laser pulses and novel composite structure

Thermoelectrically Driven Photocurrent Generation in Femtosecond Laser Patterned Graphene Junctions

Single and few-layer graphene photodetectors have attracted much attention in the past few years. Pristine graphene shows a very weak response to visible light; hence, fabrication of complex graphene-based detectors is a challenging task. In this work, we utilize the ultrafast laser functionalization of single-layer CVD graphene for highly desirable maskless fabrication of micro- and nanoscale devices. We investigate the optoelectronic response of pristine and functionalized devices under femtosecond and continuous wave lasers irradiation. We demonstrate that the photocurrent generation in p–p+ junctions formed in single-layer graphene is related to the photothermoelectric effect. The photoresponsivity of our laser patterned single-layer graphene junctions is shown to be as high as 100 mA/W with noise equivalent power less than 6 kW/cm2. These results open a path to a low-cost maskless technology for fabrication of graphene-based optoelectronic devices with tunable properties for spectroscopy, signal processing, and other applications

Advances in Nanomaterials-Based Electrochemical Biosensors for Foodborne Pathogen Detection

Electrochemical biosensors utilizing nanomaterials have received widespread attention in pathogen detection and monitoring. Here, the potential of different nanomaterials and electrochemical technologies is reviewed for the development of novel diagnostic devices for the detection of foodborne pathogens and their biomarkers. The overview covers basic electrochemical methods and means for electrode functionalization, utilization of nanomaterials that include quantum dots, gold, silver and magnetic nanoparticles, carbon nanomaterials (carbon and graphene quantum dots, carbon nanotubes, graphene and reduced graphene oxide, graphene nanoplatelets, laser-induced graphene), metal oxides (nanoparticles, 2D and 3D nanostructures) and other 2D nanomaterials. Moreover, the current and future landscape of synergic effects of nanocomposites combining different nanomaterials is provided to illustrate how the limitations of traditional technologies can be overcome to design rapid, ultrasensitive, specific and affordable biosensors. lt /p

Differential Bio-Optoelectronic Gating of Semiconducting Carbon Nanotubes by Varying the Covalent Attachment Residue of a Green Fluorescent Protein

Publisher Copyright: © 2022 The Authors. Advanced Functional Materials published by Wiley-VCH GmbHIntegrating photoactive proteins with synthetic nanomaterials holds great promise in developing optoelectronic devices whereby light, captured by a antenna protein, is converted to a modulated electrical response. The protein–nanomaterial interface is critical to defining optoelectronic properties; successful integration of bionanohybrids requires control over protein attachment site and a detailed understanding of its impact on device performance. Here, the first single-walled carbon nanotube (SWCNT) bio-optoelectronic transistor enabled by the site-specific direct interfacing with a green fluorescent protein (GFP) via genetically encoded phenyl azide photochemistry is reported. The electrical behavior of individual semiconducting SWCNTs depends on the protein residue coupling site and provides the basis to design eco-friendly phototransistors and optoelectronic memory. Attachment at one GFP residue proximal to the chromophore produces a wavelength-specific phototransistor. The bio-transistor can be switchedoff in less than 38 s with responsivity up to 7 × 103 A W−1 at 470 nm. Attachment via a second residue distal to the chromophore generates optoelectronic memory that show rapid and reproducible conductivity switching with up to 15-fold modulation that is restored on the application of a gate voltage. Therefore, photoactive proteins, especially GFP, can be realized as a key material for novel single-molecule electronic and photonic devices.Peer reviewe

Spectral-Phase Interferometry Detection of Ochratoxin A via Aptamer-Functionalized Graphene Coated Glass

In this work, we report a novel method of label-free detection of small molecules based on direct observation of interferometric signal change in graphene-modified glasses. The interferometric sensor chips are fabricated via a conventional wet transfer method of CVD-grown graphene onto the glass coverslips, lowering the device cost and allowing for upscaling the sensor fabrication. For the first time, we report the use of graphene functionalized by the aptamer as the bioreceptor, in conjunction with Spectral-Phase Interferometry (SPI) for detection of ochratoxin A (OTA). In a direct assay with an OTA-specific aptamer, we demonstrated a quick and significant change of the optical signal in response to the maximum tolerable level of OTA concentration. The sensor regeneration is possible in urea solution. The developed platform enables a direct method of kinetic analysis of small molecules using a low-cost optical chip with a graphene-aptamer sensing layer

Spectral-Phase Interferometry Detection of Ochratoxin A via Aptamer-Functionalized Graphene Coated Glass

In this work, we report a novel method of label-free detection of small molecules based on direct observation of interferometric signal change in graphene-modified glasses. The interferometric sensor chips are fabricated via a conventional wet transfer method of CVD-grown graphene onto the glass coverslips, lowering the device cost and allowing for upscaling the sensor fabrication. For the first time, we report the use of graphene functionalized by the aptamer as the bioreceptor, in conjunction with Spectral-Phase Interferometry (SPI) for detection of ochratoxin A (OTA). In a direct assay with an OTA-specific aptamer, we demonstrated a quick and significant change of the optical signal in response to the maximum tolerable level of OTA concentration. The sensor regeneration is possible in urea solution. The developed platform enables a direct method of kinetic analysis of small molecules using a low-cost optical chip with a graphene-aptamer sensing layer