Carbon Microelectromechanical Systems Research Articles

Bridging biochemistry and microengineering: glucose oxidation in microfluidic biofuel cells with carbon-MEMS and conductive polymers electrodes

Microfluidic biofuel cells are promising power sources for small-scale devices. Its construction is simple and requires low-cost materials. We report four glucose/O2 microfluidic enzymatic biofuel cells consisting in a double-Y-shaped microchannel and based on Carbon Micro Electro Mechanical Systems (C-MEMS) electrodes to test the composite poly(3,4-ethylene dioxythiophene)–poly(gallic acid) (PEDOT-PGAL) conducting polymer as an electroactive layer for enzyme immobilization. The following microfluidic enzymatic biofuel cells were microfabricated to compare their performances: 1) glucose/O2 using bioelectrodes, 2) glucose/O2 using glucose oxidase and Laccase, in solution, 3) glucose/hydrogen peroxide using bioelectrodes, and 4) glucose/hydrogen peroxide using glucose oxidase and horseradish peroxidase, in solution. The use of these two classes of materials, C-MEMS electrodes and conducting polymer inks, offers an advantageous interface for biomolecular electron transfer owing to the rich organic chemistry of the carbon interfaces. On the other hand, the conducting polymer PEDOT-PGAL acts as an electroactive layer for straightforward applications suitable for batch fabrication. All the studied cells presented positive electromotive forces and the discharge behavior of a fuel cell, yielding similar power densities. As expected, the cells that used enzymes in solution delivered higher power densities, but these values are dependent on the flow rate, while cells with immobilized enzymes present a more stable maximum power output. To our knowledge, this is the first report of an electrode system based on pyrolytic carbon/PEDOT-PGAL applied in a microfluidic enzymatic biofuel cell.

Bio-synthesized silver nanoparticle modified glassy carbon electrode as electrochemical biosensor for prostate specific antigen detection

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.

Batch Nanofabrication of Suspended Single 1D Nanoheaters for Ultralow-Power Metal Oxide Semiconductor-Based Gas Sensors.

The demand for power-efficient micro-and nanodevices is increasing rapidly. In this regard, electrothermal nanowire-based heaters are promising solutions for the ultralow-power devices required in IoT applications. Herein, a method is demonstrated for producing a 1D nanoheater by selectively coating a suspended pyrolyzed carbon nanowire backbone with a thin Au resistive heater layer and utilizing it in a portable gas sensor system. This sophisticated nanostructure is developed without complex nanofabrication and nanoscale alignment processes, owing to the suspended architecture and built-in shadow mask. The suspended carbon nanowires, which are batch-fabricated using carbon-microelectromechanical systems technology, maintain their structural and functional integrity in subsequent nanopatterning processes because of their excellent mechanical robustness. The developed nanoheater is used in gas sensors via user-designable localization of the metal oxide semiconductor nanomaterials onto the central region of the nanoheater at the desired temperature. This allows the sensing site to be uniformly heated, enabling reliable and sensitive gas detection. The 1D nanoheater embedded gas sensor can be heated immediately to 250°C at a remarkably low power of 1.6mW, surpassing the performance of state-of-the-art microheater-based gas sensors. The presented technology offers facile 1D nanoheater production and promising pathways for applications in various electrothermal devices.

Thermal conductivity detector (TCD)-type gas sensor based on a batch-fabricated 1D nanoheater for ultra-low power consumption

Thermal conductivity detectors (TCDs) are widely used to detect high-concentration gases or identify low-concentration gases in chromatography, owing to their fast response and recovery time for a wide range of gases. However, conventional TCD devices require large power consumption because of their relatively large sizes, which limits their applicability, specifically in IoT. In this study, an ultralow-power TCD was implemented for use as a gas sensor by manufacturing a suspended nanoheater via cost-effective wafer-level microfabrication technology (i.e., carbon-microelectromechanical systems). The aspect ratio of the nanoheater was optimized for a fixed minimum section area (width = 200–300 nm, thickness = 300–400 nm) using simulations and experiments. The small size, high aspect ratio (~ 270, corresponding to a nanoheater length of 80 µm), and suspended architecture allowed the nanoheater-based gas sensor to operate with high sensitivity and ultrafast response/recovery (time constant of less than 1 μs). This fast response enabled the sensor to operate with pulse-width modulation, reducing the power by 1/1000 (240 nW). The nanoheater-based gas sensor exhibited a linear gas response for various high-concentration gases (H2: 1–20 %, Ar: 1–100 %, He: 1–5 %). Moreover, the nanoheater was fabricated using only wafer-level microfabrication processes, ensuring cost-effective sensor manufacturing. Thus, nanoheater-based gas sensors are expected to be used in various portable IoT devices.

Non-faradaic electrochemical impedance spectroscopy analysis of C-MEMS derived bio-modified glassy carbon electrode

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 μl−1 DNA target. nf-EIS relies on various microscopic interactions, which occur at the electrode–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.

In-Situ Integration of 3D C-MEMS Microelectrodes with Bipolar Exfoliated Graphene for Label-Free Electrochemical Cancer Biomarkers Aptasensor.

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.

Novel Integration of Bipolar Exfoliated Graphene with 3D C-MEMS Microelectrodes for Label-Free Electrochemical Cancer Biomarkers Aptasensors

Early detection of cancer can noticeably increase the survival chance of many cancer patients. Quantifying cancer biomarkers detectable from blood is an efficient way for the early detection of cancer diseases. Among various discovered cancer biomarkers, platelet-derived growth factor-BB (PDGF-BB) is an essential biomarker for early detection of cancer and monitoring cancer patients. This biomarker plays a vital role in developing and lymphatic metastasis of solid malignant tumors such as brain, lung, breast, and liver, which enlightens the importance of developing point-of-care (POC) biosensors for the detection of PDGF-BB. In recent years, the application of synthetic DNA or RNA-based bio-recognizers (i.e., aptamers) in cancer biomarker sensor development has been vastly investigated. Electrochemical label-free aptamer-based biosensors (also known as aptasensors) are highly suitable for POC. 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. Furthermore, the surface of C-MEMS can be modified effectively via depositing nanomaterials which can enhance the electrochemical and sensing performances of the C-MEMS based biosensors. In this study, the integration of bipolar exfoliated (BPE) reduced graphene oxide (rGO) with 3D C-MEMS microelectrodes for developing PDGF-BB label-free aptasensors is investigated. A single 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 scanning electron microscopy (SEM) analysis confirms that the rGO deposited on 3D C-MEMS microelectrodes has a porous vertically aligned structure with pore sizes of around 100 nm. Cyclic voltammetry (CV) was used for characterizing the aptasensors in different stages of development and their sensing performances. The CV analysis confirms that deposition of BPE-rGO noticeably increases the capacitance of 3D C-MEMS electrodes. 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 deposition of BPE-rGO on 3D CMEMS microelectrodes. Considering the high potential of C-MEMS technology and BPE technique's simplicity and efficiency, this novel technique is highly promising for developing feasible and mass-producible lab-on-chip and point-of-care cancer diagnosis technologies.

Development of a Novel Gas-Sensing Platform Based on a Network of Metal Oxide Nanowire Junctions Formed on a Suspended Carbon Nanomesh Backbone.

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.

Thermal stress-induced fabrication of carbon micro/nanostructures and the application in high-performance enzyme-free 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.

Photolithographically-patterned C-MEMS graphene by carbon diffusion through nickel

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.

Perspectives on C-MEMS and C-NEMS biotech applications

Carbon microelectromechanical system (C-MEMS) and carbon nanoelectromechanical system (C-NEMS) have been identified as promising technologies for a range of biotech applications, including electrochemical biosensors, biofuel cells, neural probes, and dielectrophoretic cell trapping. Research teams around the world have devoted more and more time to this field. After almost two decades of efforts on developing C-MEMS and C-NEMS, a review of the relevant progress and addressing future research opportunities and critical issues is in order. This review first introduces C-MEMS and C-NEMS fabrication processes that fall into two categories: photolithography- and non-photolithography- based techniques. Next, a detailed discussion of the state of the art, and technical challenges and opportunities associated with C-MEMS and C-NEMS devices used in biotech applications are presented. These devices are discussed in the relevant sub-sections of biosensors, biofuel cells, intracorporeal neural probe, dielectrophoresis cell trapping, and cell culture. The review concludes with an exposition of future perspectives in C-MEMS and C-NEMS.

Integration of RuO2/conductive fiber composites within carbonized micro-electrode array for supercapacitors

Abstract This study employed a carbon microelectromechanical system (C-MEMS) in fabricating a 3D micro-electrode array of conductive carbon cylinders directly on the surface of a graphite substrate. The capacitance of the array was further enhanced by decorating it with a composite material comprising highly-porous carbon nanofibers (CF) and electroactive RuO2 nanoparticles to function as an active electrode. In galvanostatic charge-discharge tests, the specific capacitance of an electrode decorated with RuO2 30 wt%/CF was 219.2 F g−1 at a current density of 0.5 A g−1, which is 2.27 times higher than that of the pristine CF electrode. When the current density was increased from 0.5 A g−1 to 3 A g−1, the capacitance retention of the RuO2 30 wt%/CF electrode was 54.8%. A symmetric supercapacitor based on the RuO2 30 wt%/CF composite electrode exhibited an impressive energy density of 74.2 Wh kg−1 with power density of 4333 W kg−1. It also demonstrated good capacitance retention of 80.2% following 3000 consecutive charge/discharge cycles at a current density of 2 A g−1.

Hierarchical Porous Carbon Electrodes with Sponge-Like Edge Structures for the Sensitive Electrochemical Detection of Heavy Metals.

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).

A Three-Dimensional Hybrid Carbon-Microelectromechanical System on a Graphite-Coated Stainless Steel Substrate as a High-Performance Anode for Lithium-Ion Batteries

Three-dimensional (3D) microbatteries provide higher capacities owing to their additional volume when compared to a thin-film electrode configuration. Here for the first time, we report a carbon-mi...

Label-Free Electrochemical Aptasensors Based on Photoresist Derived Carbon for Cancer Biomarker Detection

Cancer biomarkers are substances found in the human fluid, tissue, and bone marrow that can indicate the presence of cancer diseases in the human body. In the past decades, various cancer biomarkers have been discovered for early detection of cancers and risk assessment of reoccurring cancers. Among the discovered cancer biomarkers, platelet-derived growth factor-BB (PDGF-BB) is an essential biomarker for early detection of cancer diseases. This biomarker plays a significant role in the development of multiple solid malignant tumors (e.g., breast, brain, pancreatic, prostate, and ovarian) and lymphatic metastasis. A feasible means for early detection of cancers is developing point-of-care biosensors based on synthetic DNA or RNA bio-recognizers (i.e., aptamers), which are referred to as aptasensors. Various advanced technologies have been investigated for developing cancer biomarker aptasensors, including optical, piezoelectric, and electrochemical based techniques. Among the developed technologies, label-free electrochemical aptasensors are highly potent means for this purpose since they can reduce the cost and complications of sample preparation, and the electrochemical cells can be efficiently miniaturized and integrated with available lab-on-chips and MEMS technologies. However, the sensing performance of the label-free electrochemical cancer aptasensors, including the limit of detection, selectivity, and dynamic range requires further enhancements to be at similar levels to benchtop testing. In the light of the importance of PDGF-BB detection and demanded enhancements for label-free electrochemical aptasensors, we have developed label-free electrochemical aptasensors based on photoresist derived carbon microelectrodes. The active electrode of this aptasensor was synthesized via well-established C-MEMS (carbon microelectromechanical systems) fabrication technology. C-MEMS platforms have distinguishing features such as low background capacitance, high stability when they exposed to different physical/chemical treatments, biocompatibility, and good electrical conductivity. Furthermore, the surface of C-MEMS can be modified effectively via electrochemical processes as well as depositing nanomaterials. The applied C-MEMS fabrication in this study includes photopatterning of SU-8 25 negative photoresist-based microelectrodes and carbonization of the developed microelectrodes at high temperatures and oxygen-free tube furnaces. The carbonized microelectrodes were functionalized utilizing oxygen plasma oxidation pretreatment to introduce carboxyl groups to the surfaces of the carbon microelectrodes. The PDGF-BB affinity aptamers were covalently immobilized via amid binding of amino-tag terminated aptamers and carboxyl groups covered carbon surfaces. The Fourier-transform infrared spectroscopy (FTIR) confirmed the successful carboxyl group functionalization of the C-MEMS microelectrodes and covalent immobilization of affinity aptamers via amide biding. Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) were used for characterizing the C-MEMS based aptasensors in different stages of development and sensing performances. The turn-on sensing strategy was deployed via measuring the charge transfer resistance (RCT) from EIS Nyquist plots, which yielded to wide sensing linear range of 0.005 – 50 nM with a high sensitivity of 14.82 × 103 Ω.(Log (M))-1 and low limit of detection of 1.9 pM (S/N=3). The turn-off sensing strategy was applied via measuring capacitance from CV curves, which conceded to wide linear response range of 0.01 – 50 nM with a high sensitivity of 29.97 mF.cm-2.(Log (M))-1 and low limit of detection of 7 pM (S/N=3) toward the PDGF-BB. The developed label-free electrochemical aptasensor exhibited good selectivity, stability, and repeatability, which is highly promising for future lab-on-chip and point-of-care cancer diagnosis technologies.

Highly sensitive label-free electrochemical aptasensors based on photoresist derived carbon for cancer biomarker detection

-Label-free electrochemical aptasensors for cancer biomarker detection can be a promising means for early detection of cancer due to their high sensitivity, selectivity, and stability, and low cost. In this study, a highly sensitive and selective label-free electrochemical aptasensor based on carbon microelectromechanical systems (C-MEMS) was developed for the detection of platelet-derived growth factor-BB (PDGF-BB). The active electrodes of the aptasensors were synthesized via carbonization of SU-8 derived electrodes at high temperatures in an oxygen-free furnace. An oxygen-plasma oxidation treatment was used to functionalize the C-MEMS electrodes, which provided efficient covalent immobilization of amino terminated affinity aptamers. The turn-off and turn-on detection strategies–based on capacitance and resistance measurement, respectively—were employed. The capacitance detection strategies exhibited a wide linear response range of 0.01–50 nM, with a high sensitivity of 3.33 mF cm-2 Logc-1 (unit of c, nM) and a low limit of detection of 7 pM (S/N = 3). The resistance detection strategies exhibited an even wider linear response range of 0.005–50 nM, and a lower limit of detection of 1.9 pM (S/N = 3), with a high sensitivity of 1.65 × 103 Ω Logc-1 (unit of c, nM). Both detection strategies provided high selectivity for PDGF-BB and high stability of 90.34% after 10 days. This research demonstrates that the developed label-free electrochemical C-MEMS based PDGF-BB aptasensor is highly sensitive, selective, and robust. This aptasensor is a promising prospect for the highly demanding task of early detection of cancer biomarkers.

Highly Sensitive Lactic Acid Biosensors Based on Photoresist Derived Carbon

In this study, a highly sensitive electrochemical capacitive lactic acid enzymatic sensor based on a carbon-microelectromechanical system (C-MEMS) is developed. The sensing platform of the biosensor, which is photoresist-derived carbon (PDC) microelectrode, was synthesized by pyrolysis of photo-patterned photoresist polymer in oxygen-free and high-temperature conditions. The surfaces of the microelectrodes were functionalized by the oxygen-plasma pretreatment technique to form –COOH functional groups. The lactate oxidase enzyme was immobilized on the carboxylic group covered surfaces of the microelectrodes. The sensor demonstrated the detection of lactic acid over a wide dynamic range of 0.1- $5000~\mu \text{M}$ with a low detection limit of $1.45~\mu \text{M}$ (S/N=3). The sensitivity found to be 33.48 mF.cm−2. (Log (M))−1. This mediator-free lactic acid sensor exhibited 80.07% accuracy in the presence of uric and ascorbic acid and only a 2.35% decrease of measured capacitance in 20 days, which implies good selectivity and high stability. The presented results show that the C-MEMS based lactic acid biosensor is a promising contender for the highly demanding point of care health monitoring applications.

Nano‐spaced Gold on Glassy Carbon Substrate for Controlling Cell Behavior

AbstractThis approach involves the synthesis of gold nanoparticles (GNPs) within the carbonizing photoresist (SU8) to achieve GNPs trapped glassy carbon (GNPs‐GC) substrates. Surface size distribution and interparticle separation of GNPs is primarily controlled by changing the metal precursor concentration. Chemical stability and fabrication control are achieved by selecting sodium tetrachloroaurate (NaAuCl4) over a more conventional aurochloric acid (HAuCl4) as the gold precursor. Seeding of gold nuclei in a photocrosslinking polymer is a classical representation of simultaneous homogeneous and heterogeneous nucleation. GNPs growth during the carbonization process is tracked and explained using pertinent mechanisms. With the nanoparticle spacing ranging from 260 to 50 nm, GNPs‐GC thin films are employed as interfaces for fibroblast cell adhesion. GNPs act as potential anchor points for cell adhesion and their nanoscale arrangement regulates the structural behavior of the cells. GNPs' density‐dependent fibronectin physisorption significantly improves cell adhesion and proliferation. Intraparticle spacing around 160 nm offers ideal biointerface for fibroblast attachment and spreading. Fabrication of 3D GNPs composite carbon microelectromechanical systems is achieved as a demonstration of the studied GNPs‐GC synthesis mechanism. Sub‐micron patterning of GNPs‐GC combined with its biofunctional nature presents vast opportunities in the field of bioelectronics, biophotonics, and lab/organ‐on‐a‐chip technology.

A high-energy aqueous on-chip lithium-ion capacitor based on interdigital 3D carbon microelectrode arrays

There is a growing interest in the development of high energy on-chip capacitive energy storage units for application in microelectronic devices. Lithium-ion capacitor (LIC) typically comprising battery-type and capacitor-type electrodes offer the opportunity for an improved energy density in capacitive energy storage. In this work, an aqueous on-chip LIC was fabricated using carbon microelectromechanical systems (C-MEMS) technique. Oxygen plasma-treated 3D carbon microelectrode arrays served as the capacitor-type electrode in the LIC, while LiFePO4 integrated on the 3D carbon microelectrode arrays was used as the battery-type cathode. Electrochemical performance evaluation shows that the aqueous on-chip LIC can deliver an areal density up to ~5.03 μWh cm−2, which is ~5 times higher than the oxygen plasma-treated symmetric carbon microelectrode-based electrochemical capacitor.

Microplasma direct writing for site-selective surface functionalization of carbon microelectrodes

Carbon micro- and nanoelectrodes fabricated by carbon microelectromechanical systems (carbon MEMS) are increasingly used in various biosensors and supercapacitor applications. Surface modification of as-produced carbon electrodes with oxygen functional groups is sometimes necessary for biofunctionalization or to improve electrochemical properties. However, conventional surface treatment methods have a limited ability for selective targeting of parts of a surface area for surface modification without using complex photoresist masks. Here, we report microplasma direct writing as a simple, low-cost, and low-power technique for site-selective plasma patterning of carbon MEMS electrodes with oxygen functionalities. In microplasma direct writing, a high-voltage source generates a microplasma discharge between a microelectrode tip and a target surface held at atmospheric pressure. In our setup, water vapor acts as an ionic precursor for the carboxylation and hydroxylation of carbon surface atoms. Plasma direct writing increases the oxygen content of an SU-8-derived pyrolytic carbon surface from ~3 to 27% while reducing the carbon-to-oxygen ratio from 35 to 2.75. Specifically, a microplasma treatment increases the number of carbonyl, carboxylic, and hydroxyl functional groups with the largest increase observed for carboxylic functionalities. Furthermore, water microplasma direct writing improves the hydrophilicity and the electrochemical performance of carbon electrodes with a contact-angle change from ~90° to ~20°, a reduction in the anodic peak to cathodic peak separation from 0.5 V to 0.17 V, and a 5-fold increase in specific capacitance from 8.82 mF∙cm−2 to 46.64 mF∙cm−2. The plasma direct-writing technology provides an efficient and easy-to-implement method for the selective surface functionalization of carbon MEMS electrodes for electrochemical and biosensor applications.