Xurography-Enabled Thermally Transferred Carbon Nanomaterial-Based Electrochemical Sensors on Polyethylene Terephthalate-Ethylene Vinyl Acetate Films

ElectrochemCap: an integrated detection for loop-mediated isothermal amplification reactions

Loop-mediated isothermal amplification (LAMP) of genetic materials has emerged as a powerful molecular biology technique with great potential to be a standard point-of-care (POC) technique. This method has found several applications, but it still presents challenges for its direct on-site application, particularly in terms of integrated reaction and detection systems and the risk of carryover contamination. In this work, we propose an innovative solution - an electrochemical microcentrifuge tube cap (ElectrochemCap) based on a screen-printed electrode, a 3D printed adapter and an adhesive layer - which integrates the amplification reaction and its subsequent electrochemical detection in a single device. The design, fabrication, and electrochemical characterization of the ElectrochemCap are reported here, demonstrating its suitability for LAMP detection. Rapidly emerging technologies, such as 3D printing or xurography, are the basis of a prototype that has been validated for the detection of SARS-CoV-2 using reverse transcription LAMP (RT-LAMP), achieving results comparable to those obtained by gold-standard RT-qPCR. Moreover, we have explored the versatility of the ElectrochemCap presenting several additional designs (for containers with different volumes, shapes and materials, as well as multiplexed approaches), expanding its potential applications. Overall, the ElectrochemCap represents an affordable, versatile, and marketable innovation for integrated quantitative electrochemical detection, with enormous possibilities in bioelectroanalytical procedures and portable laboratory setups.

Aptamer Based on Silver Nanoparticle-Modified Flexible Carbon Ink Printed Electrode for the Electrochemical Detection of Chikungunya Virus

Medical devices have progressed from their initial bulky forms to smart devices. However, their rigidity hampers their seamless integration into everyday life. The fields of stretchable, textile, and flexible electronics are emerging research areas with the potential to drive significant technological progress. This research presents a laboratory-based technique to produce highly sensitive and flexible biosensors for detecting the chikungunya virus. These biosensors are based on 0D nanomaterials and demonstrate significant advancements in voltammetry. The electrochemical platform was created utilizing the stencil printing (StPE) technique. Adapting the biosensor setup involved the selection of aptamer as the biorecognition element bound with silver nanoparticles (AgNPs). This biosensor was employed in the voltammetric identification of the Chikungunya virus antigen (CHIKV-Ag) within a solution containing 0.5 mM potassium ferro/ferri cyanide, a redox pair. The biosensor was employed to evaluate CHIKV-Ag within a human serum sample. It demonstrated a linear detection span ranging from 0.1 ng/mL to 1 μg/mL, with a detection limit of 0.1 ng/mL for CHIKV-Ag. The proposed approach, due to its flexibility in production and the electrocatalytic attributes displayed by the zero-dimensional nanostructure, presents innovative opportunities for cost-effective and tailored aptamer-based bioelectronics, thereby broadening the scope of this domain.

Enhanced Electron Transfer Efficiency of Fructose Dehydrogenase onto Roll-to-Roll Thermal Stamped Laser-Patterned Reduced Graphene Oxide Films

Herein, a strategy to stamp laser-produced reduced graphene oxide (rGO) onto flexible polymers using only office-grade tools, namely, roll-to-roll thermal stamping, is proposed, proving for the first time its effectiveness for direct bioelectrocatalysis. This straightforward, scalable, and low-cost approach allows us to overcome the limits of the integration of laser-induced rGO-films in bioanalytical devices. Laser-produced rGO has been thermally stamped (TS) onto different polymeric substrates (PET, PVC, and EVA) using a simple roll-laminator; the obtained TS-rGO films have been compared with the native rGO (untransferred) via morphochemical and electrochemical characterization. Particularly, the direct electron transfer (DET) reaction between fructose dehydrogenase (FDH) and TS-rGO transducers has been investigated, with respect to the influence of the amount of enzyme on the catalytic process. Remarkable differences have been observed among TS-rGO transducers; PET proved to be the elective substrate to support the transfer of the laser-induced rGO, allowing the preservation of the morphochemical features of the native material and returning a reduced capacitive current. Noteworthily, TS-rGOs ensure superior electrocatalysis using a very low amount of FDH units (15 mU). Eventually, TS-rGO-based third-generation complete enzymatic biosensors were fabricated via low-cost benchtop technologies. TS-rGOPET exhibited bioanalytical performances superior to the native rGO, allowing a sensitive (0.0289 μA cm-2 μM-1) and reproducible (RSD = 3%, n = 3) d-fructose determination at the nanomolar level (LOD = 0.2 μM). TS-rGO exploitability as a point-of-need device was proved via the monitoring of d-fructose during banana (Musa acuminata) postharvest ripening, returning accurate (recoveries 110-90%; relative error -13/+1%) and reproducible (RSD ≤ 7%; n = 3) data.

A three-dimensional composite film-modified electrode based on polyoxometalates and ionic liquid-decorated carbon nanotubes for the determination of L-tyrosine in food

A stable and innovative composite film-modified electrode based on Dawson polyoxometalates H8P2Mo16V2O62 (P2Mo16V2) and ionic liquid (BMIMBr)-decorated carbon nanotubes, annotated as PEI/(P2Mo16V2/BMIMBr-CNTs)8, has been constructed by using the layer-by-layer self-assembly (LBL) method for the determination of L-tyrosine. The combination of three active components not only offers higher conductivity to facilitate rapid electron transfer, but also avoids the accumulation of P2Mo16V2 to expand the contact area and increase the reactive active sites. The modified electrode exhibits outstanding sensing performance for determination of Tyr with wide linear determination range of 5.8×10-7 M ~ 1.2×10-4 M, low determination limit of 1.7×10-7M (S/N=3), high selectivity for common interferences, and excellent stability at the potential of +0.78 V (vs. Ag/AgCl (3 M KCl)). The relative standard deviation (RSD) of 4.3% for five groups of parallel experiments shows the satisfactory repeatability of PEI/(P2Mo16V2/BMIMBr-CNTs)8. In addition, for determination of Tyr, the PEI/(P2Mo16V2/BMIMBr-CNTs)8 shows good recoveries of 98.8-99.8% in meat floss, which can be feasible in practical application.

Freestanding laser-induced two dimensional heterostructures for self-contained paper-based sensors

The production of 2D/2D heterostructures (HTs) with favorable electrochemical features is challenging, particularly for semiconductor transition metal dichalcogenides (TMDs). In this studies, we introduce a CO₂ laser plotter-based technology for the realization of HT films comprising reduced graphene oxide (rGO) and 2D-TMDs (MoS₂, WS₂, MoSe₂, and WSe₂) produced via water phase exfoliation. The strategy relies on the Laser-Induced production of HeterosTructures (LIHTs), where after irradiation the nanomaterials exhibit changes in the morphological and chemical structure, becoming conductive easily transferable nanostructured films. The LIHTs were characterized in detail by SEM, XPS, Raman and electrochemical analysis. The laser treatment induces the conversion of GO into conductive highly exfoliated rGO decorated with homogeneously distributed small TMD/TM-oxide nanoflakes. The freestanding LIHT films obtained were employed to build self-contained sensors onto nitrocellulose, where the HT works both as a transducer and sensing surface. The proposed nitrocellulose-sensor manufacturing process is semi-automated and reproducible, multiple HT films may be produced in the same laser treatment and the stencil-printing allows customizable design. Excellent performance in the electroanalytical detection of different molecules such as dopamine (a neurotransmitter), catechin (a flavonol), and hydrogen peroxide was demonstrated, obtaining nanomolar limits of detection and satisfactory recovery rates in biological and agrifood samples, together with high fouling resistance. Considering the robust and rapid laser-induced production of HTs and the versatility of scribing desired patterns, the proposed approach appears as a disruptive technology for the development of electrochemical devices through sustainable and accessible strategies.

Rapid pretreatment-free evaluation of antioxidant capacity in extra virgin olive oil using a laser-nanodecorated electrochemical lab-on-strip

An electroanalytical lab-on-a-strip device for the direct extra-virgin olive oil (EVOO) antioxidant capacity evaluation is proposed. The lab-made device is composed of a CO₂ laser nanodecorated sensor combined with a cutter-plotter molded paper-strip designed for EVOOs sampling and extraction. Satisfactory performance towards the most representative o-diphenols of EVOOs i.e., hydroxytyrosol (HY) and oleuropein (OL) were achieved; good sensitivity (LOD_HY = 2 µM; LOD_OL = 0.6 µM), extended linear ranges (HY: 10-250 µM; OL: 2.5-50 µM) and outstanding reproducibility (RSD < 5%, n = 3) were obtained in rectified oil. The device was challenged for the extraction-free analysis of 15 different EVOO samples, with satisfactory recoveries (90-94%; RSD < 5%, n = 3) and correlation with classical photometric assays (r ≥ 0.91). The proposed device includes all analysis steps, needs 4 µL of sample, and returns reliable results in 2 min, resulting portable and usable with a smartphone.

Carbon Black Functionalized with Naturally Occurring Compounds in Water Phase for Electrochemical Sensing of Antioxidant Compounds

A new sustainable route to nanodispersed and functionalized carbon black in water phase (W-CB) is proposed. The sonochemical strategy exploits ultrasounds to disaggregate the CB, while two selected functional naturally derived compounds, sodium cholate (SC) and rosmarinic acid (RA), act as stabilizing agents ensuring dispersibility in water adhering onto the CB nanoparticles’ surface. Strategically, the CB-RA compound is used to drive the AuNPs self-assembling at room temperature, resulting in a CB surface that is nanodecorated; further, this is achieved without the need for additional reagents. Electrochemical sensors based on the proposed nanomaterials are realized and characterized both morphologically and electrochemically. The W-CBs’ electroanalytical potential is proved in the anodic and cathodic window using caffeic acid (CF) and hydroquinone (HQ), two antioxidant compounds that are significant for food and the environment. For both antioxidants, repeatable (RSD ≤ 3.3%; n = 10) and reproducible (RSD ≤ 3.8%; n = 3) electroanalysis results were obtained, achieving nanomolar detection limits (CF: 29 nM; HQ: 44 nM). CF and HQ are successfully determined in food and environmental samples (recoveries 97–113%), and also in the presence of other phenolic classes and HQ structural isomers. The water dispersibility of the proposed materials can be an opportunity for (bio) sensor fabrication and sustainable device realization.

Modular graphene mediator film-based electrochemical pocket device for chlorpyrifos determination

In this work, a redox-graphene (Rx-Gr) film with electron-mediating ability has been integrated into a modular flexible pocket device, giving rise to a reusable biosensing platform. The Rx-Gr has been obtained in water from graphite taking advantage of catechin, a redox-antioxidant, able to assist the sonochemical layered-material exfoliation, conferring electron mediating feature. A film composed exclusively of Rx-Gr has been transferred via thermal rolling onto a flexible PET-support that was used as the biosensor base. The biosensing platform, composed of office-grade materials, was then fabricated using a cutter-plotter and assembled by thermal lamination; an interchangeable paper-based strip was used to host the enzymatic reaction and drive the capillary flow. An acetylcholinesterase-based inhibition assay has been optimized onboard the pocket device to determine chlorpyriphos, a widespread environmental pesticide. The proposed set-up allows the determination of chlorpyriphos at low overpotential (0.2 V) with satisfactory sensitivity (LOD = 0.2 ppb), thanks to the straightforward electroactivity of the Rx-Gr film towards thiocholine (enzymatic product). The modular design allows 5 consecutive complete inhibition assays (control + inhibition measure) retaining the performance (RSD = 5.4%; n = 5). The coupling of bench-top technologies and a new functional graphene film resulted in the development of a cost-effective, reusable, transportable, and within everyone's reach biosensing platform.

Versatile and Easily Designable Polyester-Laser Toner Interfaces for Site-Oriented Adsorption of Antibodies

Laser toners appear as attractive materials for barriers and easily laminated interphases for Lab-on-a-Foil microfluidics, due to the excellent adhesion to paper and various membranes or foils. This work shows for the first time a comprehensive study on the adsorption of antibodies on toner-covered poly(ethylene terephthalate) (PET@toner) substrates, together with assessment of such platforms in rapid prototyping of disposable microdevices and microarrays for immunodiagnostics. In the framework of presented research, the surface properties and antibody binding capacity of PET substrates with varying levels of toner coverage (0–100%) were characterized in detail. It was proven that polystyrene-acrylate copolymer-based toner offers higher antibody adsorption efficiency compared with unmodified polystyrene and PET as well as faster adsorption kinetics. Comparative studies of the influence of pH on the effectiveness of antibodies immobilization as well as measurements of surface ζ-potential of PET, toner, and polystyrene confirmed the dominant role of hydrophobic interactions in adsorption mechanism. The applicability of PET@toner substrates as removable masks for protection of foil against permanent hydrophilization was also shown. It opens up the possibility of precise tuning of wettability and antibody binding capacity. Therefore, PET@toner foils are presented as useful platforms in the construction of immunoarrays or components of microfluidic systems.

Metal nanoparticles based lab-on-paper for phenolic compounds evaluation with no sample pretreatment. Application to extra virgin olive oil samples

In this work, a low-cost, disposable, and portable lab-on-paper device is proposed to simultaneously quantify total polyphenol content (TPC) and antioxidant capacity (AOC) in 15 min; the assay requires no pre-treatment of the samples. The lab-on-paper device fabrication has been carried out employing a xurography-based benchtop microfabrication technology using low-cost materials as chromatography paper and polymeric sheets. Extra virgin olive oil (EVOO) phenolic compounds' represents a nutritional added value, nevertheless, the high lipidic content hinders their direct and rapid analysis, resulting in an extremely challenging sample. The realized lab-on-paper allows to perform the dual TPC and AOC determination in three simple steps: (i) sample loading, (ii) analytes transport to the analysis spot, and (iii) double colorimetric analysis exploiting the growth of AuNPs and AgNPs on paper mediated by phenolic compounds. Signal acquisition is achieved using a standard digital camera. The dual colorimetric assay is able to detect phenolic compounds in the 25-500 mg L^-1 range with limits of detection ≤6 mg L^-1 and good reproducibility (RSDs ≤11%). Direct analysis of EVOO samples (n = 30) correlated well (r > 0.92) with conventional spectrophotometric methods for TPC and AOC determination.

(+)-Catechin-assisted graphene production by sonochemical exfoliation in water. A new redox-active nanomaterial for electromediated sensing

A new green and effective sonochemical liquid-phase exfoliation (LPE) is proposed wherein a flavonoid compound, catechin (CT), promotes the formation of conductive, redox-active, water-phase stable graphene nanoflakes (GF). To maximize the GF-CT redox activity, the CT concentration and sonication time have been studied, and the best performing nanomaterial-fraction selected. Physicochemical and electrochemical methods have been employed to characterize the morphological, structural, and electrochemical features of the GF-CT nanoflakes. The obtained GF intercalated with CT exhibits fully reversible electrochemistry (ΔEp = 28 mV, ipa/ipc = ⁓1) because of the catecholic adducts. GF-CT-integrated electrochemistry was generated directly during LPE of graphite, with no need of graphene oxide production, nor activation steps, electropolymerization, or ex-post functionalization. The GF-CT electro-mediator ability has been proven towards hydrazine (HY) and β-nicotinamide adenine dinucleotide (NADH) by simply drop-casting the redox-material onto screen-printed electrodes. GF-CT-based electrodes by using amperometry exhibited high sensitivity and extended linear ranges (HY: LOD = 0.1 µM, L.R. 0.5-150 µM; NADH: LOD = 0.6 µM, L.R. 2.5-200 µM) at low overpotential (+ 0.15 V) with no electrode fouling. The GF-CT electrodes are performing significantly better than commercial graphite electrodes and graphene nanoflakes exfoliated with a conventional surfactant, such as sodium cholate. Recoveries of 94-107% with RSD ≤ 8% (n = 3) for determination of HY and NADH in environmental and biological samples were achieved, proving the material functionality also in challenging analytical media. The presented GF-CT is a new functional redox-active material obtainable with a single-pot sustainable strategy, exhibiting standout properties particularly prone to (bio)sensors and cutting-edge device development.