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Prostate cancer is the second leading cause of death for men after lung cancer. Therefore, early detection of cancer proteins or biomarkers is crucial in assessing the disease's reappearance after treatment. Here, we have reported the glassy carbon electrode (GCE) based electrochemical biosensors fabricated using Carbon-Microelectromechanical Systems (C-MEMS) technology for prostate-specific antigen (PSA) quantification. This report also presents the biosensor improvement by modifying the GCE with silver nanoparticles (AgNPs). Moreover, our investigation extends to bio-synthesized AgNPs that bring together advantageous chemical and physical attributes at a reasonable cost. In addition, AgNPs modified GCE have a more comprehensive anodic potential range [˗0.2 V to +0.3 V] than bare glassy carbon (GC). Electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) measurements were used to examine the electrochemical response of the biosensors. As a result of the use of AgNPs-modified GCE, we have developed a label-free analytical system for prostate cancer detection, which can provide a linear response in the concentration range of 1 pg/ml - 3 µg/ml in a reasonably simple operation. The developed biosensors may be used for the early detection of prostate cancer in clinical analysis due to the excellent sensitivity demonstrated by this electrochemical biosensor.

In this work, we have developed a carbon-microelectromechanical systems derived glassy carbon electrode (GCE) for non-faradaic electrochemical impedance spectroscopy (nf-EIS) measurement to detect electrode interfacial changes upon biomodification. This is carried out using a three-electrode system configuration. The fabricated electrode was electrochemically characterized in phosphate-buffered solution, and then changes in impedance were observed upon bio-modification of the electrode surface. The absence of any labelling molecule and no redox indicators makes the measurement system more straightforward and precise. The investigations were done using a standard deoxyribonucleic acid (DNA) immobilization on the GCE. The surface modification was done using a two-step assembly protocol linking the probe to the carbon electrode and blocking the unwanted sites using a spacer chemical-mercaptohexanol. The results obtained help us to understand the electrical signatures upon bio-modification of electrodes in the presence of a probe and its complementary 50 ng ÎĽ lâˆ'1 DNA target. nf-EIS relies on various microscopic interactions, which occur at the electrodeâ€"electrolyte interface system. We are currently working on extending this study to develop a precise, accurate and sensitive sensor to detect bio-molecular interactions occurring on the GCE to detect disease-causing microorganisms in contaminated water samples. [ABSTRACT FROM AUTHOR]

In this work, we have prepared glassy carbon electrodes using conventional carbon-microelectromechanical (C-MEMS) process. SU-8 photoresist has been used as the carbon precursor. The carbon thin film electrodes have then been tested by cyclic voltammetry measurements in the potential range of −800 mV to 800 mV vs Ag/AgCl electrode in presence of 10 mM potassium ferricyanide solution, without any functionalization. The samples have also been immobilized with anti-Hepatitis-B surface antigen (HBsAg) monoclonal antibody by physical adsorption. The presence of antibodies has been further confirmed by UV-VIS spectrophotometry. It has been observed that the current peak reduces distinctly and the fractional change in current magnitude is around 33% and 75% at the potential of 175 mV vs Ag/AgCl electrode for 10 fM and 100 fM concentration respectively. Hence, the presented study is the proof-of concept of electrochemical sensing behavior of HBsAg using functionalized glassy carbon electrodes which when integrated with low cost microfluidic platform can be suitable for point-of-care diagnostics. [ABSTRACT FROM AUTHOR]

The electrochemical label-free aptamer-based biosensors (also known as aptasensors) are highly suitable for point-of-care applications. The well-established C-MEMS (carbon microelectromechanical systems) platforms have distinguishing features which are highly suitable for biosensing applications such as low background noise, high capacitance, high stability when exposed to different physical/chemical treatments, biocompatibility, and good electrical conductivity. This study investigates the integration of bipolar exfoliated (BPE) reduced graphene oxide (rGO) with 3D C-MEMS microelectrodes for developing PDGF-BB (platelet-derived growth factor-BB) label-free aptasensors. A simple setup has been used for exfoliation, reduction, and deposition of rGO on the 3D C-MEMS microelectrodes based on the principle of bipolar electrochemistry of graphite in deionized water. The electrochemical bipolar exfoliation of rGO resolves the drawbacks of commonly applied methods for synthesis and deposition of rGO, such as requiring complicated and costly processes, excessive use of harsh chemicals, and complex subsequent deposition procedures. The PDGF-BB affinity aptamers were covalently immobilized by binding amino-tag terminated aptamers and rGO surfaces. The turn-off sensing strategy was implemented by measuring the areal capacitance from CV plots. The aptasensor showed a wide linear range of 1 pM–10 nM, high sensitivity of 3.09 mF cm−2 Logc−1 (unit of c, pM), and a low detection limit of 0.75 pM. This study demonstrated the successful and novel in-situ deposition of BPE-rGO on 3D C-MEMS microelectrodes. Considering the BPE technique’s simplicity and efficiency, along with the high potential of C-MEMS technology, this novel procedure is highly promising for developing high-performance graphene-based viable lab-on-chip and point-of-care cancer diagnosis technologies.

Junction networks made of longitudinally connected metal oxide nanowires (MOx NWs) have been widely utilized in resistive-type gas sensors because the potential barrier at the NW junctions leads to improved gas sensing performances. However, conventional MOx–NW-based gas sensors exhibit limited gas access to the sensing sites and reduced utilization of the entire NW surfaces because the NW networks are grown on the substrate. This study presents a novel gas sensor platform facilitating the formation of ZnO NW junction networks in a suspended architecture by growing ZnO NWs radially on a suspended carbon mesh backbone consisting of sub-micrometer-sized wires. NW networks were densely formed in the lateral and longitudinal directions of the ZnO NWs, forming additional longitudinally connected junctions in the voids of the carbon mesh. Therefore, target gases could efficiently access the sensing sites, including the junctions and the entire surface of the ZnO NWs. Thus, the present sensor, based on a suspended network of longitudinally connected NW junctions, exhibited enhanced gas response, sensitivity, and lower limit of detection compared to sensors consisting of only laterally connected NWs. In addition, complete sensor structures consisting of a suspended carbon mesh backbone and ZnO NWs could be prepared using only batch fabrication processes such as carbon microelectromechanical systems and hydrothermal synthesis, allowing cost-effective sensor fabrication.

Through-silicon via (TSV) is a key packaging technology that facilitates the 2.5D/3D integration of microelectromechanical system (MEMS) devices. Among various MEMS technologies, C-MEMS enables micro/nanoscale 3D carbon structure manufacturing using high-temperature (600–1200 °C) pyrolysis. These high-temperature conditions limit the application of conventional TSV technologies to C-MEMS devices. This study presents a novel TSV with carbon via-sealing plates that are adaptable to C-MEMS device packaging. Via holes are drilled before integrating the MEMS device to protect the delicate micro/nanoscale structures. Moreover, the topside via inlet is sealed with a thin conductive pyrolyzed carbon plate to prevent the contamination of the via interior during the C-MEMS process and ensure an electrical connection between the devices and the vias. After integrating the C-MEMS devices, TSV fabrication is completed by coating the via inside with a metal layer from the wafer's bottom side, achieving a conductance per unit area of approximately 327 S/mm2 (via diameter = 33 μm, length = 100 μm). The applicability of the proposed wafer-level TSV technology to C-MEMS devices is then verified through the implementation of a suspended carbon nanowire-based gas sensor integrated with the developed TSV, which exhibits excellent signal transmission. Furthermore, the proposed TSV packaging technology can be applied to various micro/nanofabrication technologies because of its high-temperature/wet-process compatibility and cost-effective fabrication. [Display omitted] • Novel high-temperature adaptive TSV technology with pyrolyzed carbon sealing plates. • Via holes are pre-drilled to protect delicate micro/nanoscale carbon devices. • Topside via inlet is sealed with a thin conductive pyrolyzed carbon plate. • The unique sealing plate is achieved by pyrolyzing freestanding photoresist film. • The proposed TSV has been verified using a carbon nanowire-based gas sensor. [ABSTRACT FROM AUTHOR]

This article presents the development of a highly sensitive electrochemical heavy metal sensor based on hierarchical porous carbon electrodes with sponge-like edge structures. Micrometer-scale hierarchical nanoporous carbon electrodes were fabricated at a wafer-scale using cost-effective batch microfabrication technologies, including the carbon microelectromechanical systems technology and oxygen plasma etching. The sponge-like hierarchical porous structure and sub-micrometer edges of the nanoporous carbon electrodes facilitate fast electron transfer rate and large active sites, leading to the efficient formation of dense heavy metal alloy particles of small sizes during the preconcentration step. This enhanced the peak current response during the square wave anodic stripping voltammetry, enabling the detection of Cd(II) and Pb(II) at concentrations as low as 0.41 and 0.7 μg L−1, respectively, with high sensitivity per unit sensing area (Cd: 109.45 nA μg−1 L mm−2, Pb: 100.37 nA μg−1 L mm−2).

We developed an electrochemical redox cycling-based immunosensor using a 3D carbon system consisting of a suspended mesh and substrate-bound interdigitated array (IDA) nanoelectrodes. The carbon structures were fabricated using a simple, cost-effective, and reproducible microfabrication technology known as carbon microelectromechanical systems (C-MEMS). We demonstrated that the 3D sub-micrometer-sized mesh architecture and selective modification of the suspended mesh facilitated the efficient production of large quantities of electrochemical redox species. The electrochemically active surfaces and small size of IDA nanoelectrodes with a 1:1 aspect ratio exhibited high signal amplification resulting from efficient redox cycling of electrochemical species (PAP/PQI) by a factor of ~25. The proposed selective surface modification scheme facilitated efficient redox cycling and exhibited a linear detection range of 0.001–100 ng/mL for cardiac myoglobin (cMyo). The specific detection of cMyo was also achieved in the presence of other interfering species. Moreover, the proposed 3D carbon system-based immunosensor successfully detected as low as ~0.4 pg/mL cMyo in phosphate-buffered saline and human serum. [ABSTRACT FROM AUTHOR]

SU-8 is a negative photoresist that is widely used as a precursor to carbon in the fabrication of 3D carbon microstructures. These microstructures are used in applications including sensors, manipulators and batteries. The SU-8 structures are usually made using photolithography and heat treated to high temperatures in an inert atmosphere to achieve carbonization. The shrinkage that results during carbonization affects the design of devices where these structures are used. In this work we studied the shrinkage during carbonization. We emphasized the impact of 1) carbonization protocol and 2) geometry and shape of the SU-8 precursor. Using statistical analysis with ANOVA, we concluded that the geometry of the structure, pyrolysis temperature and pyrolysis atmosphere play a major role in determining the shrinkage of the SU-8 structures. We did not observe a statistically-valid impact from changes in dwell times and heating rate. Based on these results, we present a series of relations to help predict the shrinkage of SU-8 microstructures during carbonization, and facilitate the design of carbon 3D microstructures in different fields. [ABSTRACT FROM AUTHOR]

Abstract: Herein, we present a novel electrochemical sensing platform that consists of a set of suspended carbon nanowire-based mesh electrode with deliberately controlled shapes (hexagonal or diamond), and a substrate-bound planar carbon electrode. These electrodes overlapped one another with a pre-defined gap which was precisely controlled by using a polymerization-stop layer. By recycling the redox reactions between the electrodes with a 2.1-μm-gap, the redox current of Fe(CN)6 4−/Fe(CN)6 3− could be amplified approximately 37 times. This high current amplifying capability enabled dopamine detection down to 5μM using cycling voltammetry. The complex morphology of the stacked carbon structures was obtained by simply using multiple UV-lithography processes and a single pyrolysis process that allowed pre-defined polymer structures to shrink into sub-micrometer-scale carbon structures. The suspended carbon mesh structures confined the mass-transfer near the electrode overlap region, and hence, the electrode set operated as a “sandwich” electrode enclosed within a microchannel. This effect was studied by simulating the mass transfer of the redox species, and confirmed by electrochemical measurements. [Copyright &y& Elsevier]

Highlights: [•] Glucose sensor with C-MEMS/carbon nanotubes integrated electrode was fabricated. [•] The modification of carbon nanotubes improves the sensitivity about 50 times. [•] The response time is less than 10s with linear range from 5 to 80mM. [Copyright &y& Elsevier]

Abstract: Three-dimensional pyrolyzed carbon micropatterns were fabricated by using photolithography and pyrolysis process. Direct amination was achieved by functionalizing its surface with ultraviolet (UV) irradiation under ammonia gas. Quantified amino groups on the carbon surface were estimated by X-ray photoelectron spectroscopy. Hybridization intensity and intensity profile were investigated by epifluorescence microscopy. [Copyright &y& Elsevier]

Abstract: Prototypes of photosynthetic-bacterium micro-biofuel cells have been developed in our laboratory, in which electrons are extracted from bacterial cells while they are in contact with an electrode. The material and shape of the electrode should be electroconductive and biocompatible with a low electrical resistance and a high-specific surface area, therefore, pyrolyzed carbon was fabricated either to a flat or porous surface electrode using carbon microelectromechanical systems (C-MEMS). The developed electrodes were applied in micro-biofuel cells, and the porous electrode showed a fourfold higher performance than the flat one. [Copyright &y& Elsevier]

Abstract: This paper details the fabrication and testing of a fuel cell stack using a novel manufacturing approach for creating carbon bipolar plates. The fundamental fabrication techniques have been described in a previous contribution [1]. The initial paper characterized a single cell. In this work, the fabrication techniques are utilized to fabricate a three-cell fuel cell stack. Operating data in different operating conditions is measured and presented. Information on cell performance at different operating temperatures and pressures is included. The methodology for the fuel cell characterization is presented. [Copyright &y& Elsevier]

Abstract: Carbonization of machined polymers is a method of creating carbon structures with small feature sizes without having to directly machine carbon (a difficult and expensive process). Pyrolyzed carbon fluidic plates with feature sizes less than 1mm are used to create a miniature fuel cell. Epoxy is used to seal the fuel cell and water is directly applied to exposed Nafion® to hydrate the membrane. The use of miniature carbon fluidic plates will allow for fabrication of 3D (non-planar) proton exchange membrane fuel cells utilizing carbon bipolar plates. Initial test results of the fuel cell are given. [Copyright &y& Elsevier]

The electrochemical label-free aptamer-based biosensors (also known as aptasensors) are highly suitable for point-of-care applications. The well-established C-MEMS (carbon microelectromechanical systems) platforms have distinguishing features which are highly suitable for biosensing applications such as low background noise, high capacitance, high stability when exposed to different physical/chemical treatments, biocompatibility, and good electrical conductivity. This study investigates the integration of bipolar exfoliated (BPE) reduced graphene oxide (rGO) with 3D C-MEMS microelectrodes for developing PDGF-BB (platelet-derived growth factor-BB) label-free aptasensors. A simple setup has been used for exfoliation, reduction, and deposition of rGO on the 3D C-MEMS microelectrodes based on the principle of bipolar electrochemistry of graphite in deionized water. The electrochemical bipolar exfoliation of rGO resolves the drawbacks of commonly applied methods for synthesis and deposition of rGO, such as requiring complicated and costly processes, excessive use of harsh chemicals, and complex subsequent deposition procedures. The PDGF-BB affinity aptamers were covalently immobilized by binding amino-tag terminated aptamers and rGO surfaces. The turn-off sensing strategy was implemented by measuring the areal capacitance from CV plots. The aptasensor showed a wide linear range of 1 pM–10 nM, high sensitivity of 3.09 mF cm−2 Logc−1 (unit of c, pM), and a low detection limit of 0.75 pM. This study demonstrated the successful and novel in-situ deposition of BPE-rGO on 3D C-MEMS microelectrodes. Considering the BPE technique's simplicity and efficiency, along with the high potential of C-MEMS technology, this novel procedure is highly promising for developing high-performance graphene-based viable lab-on-chip and point-of-care cancer diagnosis technologies. [ABSTRACT FROM AUTHOR]

• Fabrication of novel flower-like carbon micro/nanostructures. • Carbon micro/nanostructures were induced by thermal stresses during pyrolysis of suspended photoresist structures. • Flower-like carbon micro/nanostructures were integrated with CuO nanoflims. • The CuO/carbon micro/nanostructures were demonstrated as sensitive nonenzymatic glucose sensors. Enzyme-free glucose sensors are of great significance for monitoring patients' blood glucose, but the fabrication of high performance sensors is still challenging. Carbon micro/nanostructures are good candidates for enzyme-free glucose sensors due to good biocompatibility and conductivity, and highly active surface area. In this study, the formation of flower-like carbon micro/nanostructure arrays by the thermal stress from pyrolysis of suspended micro/nanostructures was studied. The modified carbon microelectromechanical system (C-MEMS) technology involved overexposure of photoresist structures, oxygen plasma etching and pyrolysis processes with stainless steel as substrate. The effects of fabrication parameters like exposure time and width of suspended part to the formation of carbon micro/nanostructures were discussed. The novel carbon micro/nanostructures were integrated with copper oxide (CuO) nanofilm for the application of enzyme-free glucose sensors. The electrochemical performances of CuO nanofilm/carbon micro/nanostructures were characterized, and the results showed that the enzymeless glucose sensors demonstrated excellent specificity, good stability, high sensitivity of (1.09 ± 0.05)×103 μA mM−1 cm−2 and low detection limit of 4.51 ± 0.03 μM. The obtained micro/nanostructures have great potential for high performance micro sensors and on-chip energy storage devices, and the presented approach is promising for large-scale manufacturing of carbon micro/nanostructures. [ABSTRACT FROM AUTHOR]

Junction networks made of longitudinally connected metal oxide nanowires (MOx NWs) have been widely utilized in resistive-type gas sensors because the potential barrier at the NW junctions leads to improved gas sensing performances. However, conventional MOx–NW-based gas sensors exhibit limited gas access to the sensing sites and reduced utilization of the entire NW surfaces because the NW networks are grown on the substrate. This study presents a novel gas sensor platform facilitating the formation of ZnO NW junction networks in a suspended architecture by growing ZnO NWs radially on a suspended carbon mesh backbone consisting of sub-micrometer-sized wires. NW networks were densely formed in the lateral and longitudinal directions of the ZnO NWs, forming additional longitudinally connected junctions in the voids of the carbon mesh. Therefore, target gases could efficiently access the sensing sites, including the junctions and the entire surface of the ZnO NWs. Thus, the present sensor, based on a suspended network of longitudinally connected NW junctions, exhibited enhanced gas response, sensitivity, and lower limit of detection compared to sensors consisting of only laterally connected NWs. In addition, complete sensor structures consisting of a suspended carbon mesh backbone and ZnO NWs could be prepared using only batch fabrication processes such as carbon microelectromechanical systems and hydrothermal synthesis, allowing cost-effective sensor fabrication. [ABSTRACT FROM AUTHOR]

This article presents the development of a highly sensitive electrochemical heavy metal sensor based on hierarchical porous carbon electrodes with sponge-like edge structures. Micrometer-scale hierarchical nanoporous carbon electrodes were fabricated at a wafer-scale using cost-effective batch microfabrication technologies, including the carbon microelectromechanical systems technology and oxygen plasma etching. The sponge-like hierarchical porous structure and sub-micrometer edges of the nanoporous carbon electrodes facilitate fast electron transfer rate and large active sites, leading to the efficient formation of dense heavy metal alloy particles of small sizes during the preconcentration step. This enhanced the peak current response during the square wave anodic stripping voltammetry, enabling the detection of Cd(II) and Pb(II) at concentrations as low as 0.41 and 0.7 μg L−1, respectively, with high sensitivity per unit sensing area (Cd: 109.45 nA μg−1 L mm−2, Pb: 100.37 nA μg−1 L mm−2). [ABSTRACT FROM AUTHOR]

In recent years the most studied carbon allotrope has been graphene, due to the outstanding properties that this two-dimensional material exhibits; however, it turns out to be a difficult material to produce, pattern, and transfer to a device substrate without contamination. Carbon microelectromechanical systems are a versatile technology used to create nano/micro carbon devices by pyrolyzing a patterned photoresist, making them highly attractive for industrial applications. Furthermore, recent works have reported that pyrolytic carbon material can be graphitized by the diffusion of carbon atoms through a transition metal layer. In this work we take advantage of the latter two methods in order to produce multilayer graphene by improving the molecular ordering of photolithographically-defined pyrolytic carbon microstructures, through the diffusion (annealing) of carbon atoms through nickel, and also to eliminate any further transfer process to a device substrate. The allotropic nature of the final carbon microstructures was inspected by Raman spectroscopy (Average I D / I G of 0.2348 ± 0.0314) and TEM clearly shows well-aligned lattice planes of 3.34 Å fringe separation. These results were compared to measurements made on pyrolytic carbon (Average I D / I G of 0.9848 ± 0.0235) to confirm that our method is capable of producing a patterned multilayer graphene material directly on a silicon substrate., (© 2021 IOP Publishing Ltd.)