Breaking the barrier to biomolecule limit-of-detection via 3D printed multi-length-scale graphene-coated electrodes

Advancing transistor-based point-of-care (POC) biosensors: additive manufacturing technologies and device integration strategies for real-life sensing

Infectious pathogens pose a significant threat to public health and healthcare systems, making the development of a point-of-care (POC) detection platform for their early identification a key focus in recent decades. Among the numerous biosensors developed over the years, transistor-based biosensors, particularly those incorporating nanomaterials, have emerged as promising candidates for POC detection, given their unique electronic characteristics, compact size, broad dynamic range, and real-time biological detection capabilities with limits of detection (LODs) down to zeptomolar levels. However, the translation of laboratory-based biosensors into practical applications faces two primary challenges: the cost-effective and scalable fabrication of high-quality transistor sensors and functional device integration. This review is structured into two main parts. The first part examines recent advancements in additive manufacturing technologies-namely in screen printing, inkjet printing, aerosol jet printing, and digital light processing-and evaluates their applications in the mass production of transistor-based biosensors. While additive manufacturing offers significant advantages, such as high quality, cost-effectiveness, rapid prototyping, less instrument reliance, less material waste, and adaptability to diverse surfaces, challenges related to uniformity and yield remain to be addressed before these technologies can be widely adopted for large-scale production. The second part focuses on various functional integration strategies to enhance the practical applicability of these biosensors, which is essential for their successful translation from laboratory research to commercialization. Specifically, it provides a comprehensive review of current miniaturized lab-on-a-chip systems, microfluidic manipulation, simultaneous sampling and detection, wearable implementation, and integration with the Internet of Things (IoT).

Sustainable Materials Enabled Terahertz Functional Devices

Terahertz (THz) devices, owing to their distinctive optical properties, have achieved myriad applications in diverse domains including wireless communication, medical imaging therapy, hazardous substance detection, and environmental governance. Concurrently, to mitigate the environmental impact of electronic waste generated by traditional materials, sustainable materials-based THz functional devices are being explored for further research by taking advantages of their eco-friendliness, cost-effective, enhanced safety, robust biodegradability and biocompatibility. This review focuses on the origins and distinctive biological structures of sustainable materials as well as succinctly elucidates the latest applications in THz functional device fabrication, including wireless communication devices, macromolecule detection sensors, environment monitoring sensors, and biomedical therapeutic devices. We further highlight recent applications of sustainable materials-based THz functional devices in hazardous substance detection, protein-based macromolecule detection, and environmental monitoring. Besides, this review explores the developmental prospects of integrating sustainable materials with THz functional devices, presenting their potential applications in the future.

Engineering 3D microtip gates of all-polymer organic electrochemical transistors for rapid femtomolar nucleic-acid-based saliva testing

Point-of-care testing (POCT) of trace amount of biomarkers in biofluids is critical towards health monitoring and early diagnosis. In particular, to facilitate non-invasive saliva testing, the development of low-cost, lightweight and disposable biosensors is in urgent need, while the ultrahigh sensitivity beyond conventional clinical tests remains a great challenge. Herein, we demonstrate a simple and fully printable all-polymer organic electrochemical transistor (OECT) biosensor to detect femtomolar (fM)-level biomolecules in saliva within a few minutes by employing highly conducting lithium bis(trifluoromethanesulfonyl)imide (LiTFSI)-doped poly(3,4-ethylenedioxythiophene):poly(4-styrenesulfonate) (PEDOT:PSS) serving as both the channel and gate. A 3D microtip-shaped and Au nanoparticle-decorated multiscale gate interface facilitates the sub-fM-level sensing of female hormones (e.g., progesterone) and oligonucleotide cancer biomarkers by aptamers and DNA probes, respectively. Compared to a planar gate, the micro-engineered interface endows the OECT biosensor with significantly lower detection limit by 10-100 times down to <0.1 fM and faster response of <5 min, accomplishing unprecedentedly high sensitivity while maintaining outstanding mechanical flexibility. Consequently, such microtip-gate all-polymer OECT (MAOECT) enables POCT directly in 1000-fold diluted human saliva samples without centrifugation or redox probes, benefiting female fertility monitoring and oral cancer diagnosis as proof-of-concept demonstrations. This straightforward approach presents great potentials in low-cost wearable health management, at-home monitoring and personalized medicine.

3D-AJP: Fabrication of Advanced Microarchitected Multimaterial Ceramic Structures via Binder-Free and Auxiliary-Free Aerosol Jet 3D Nanoprinting

Manufacturing of ceramics is challenging due to their low toughness and high hardness. Additive Manufacturing (AM) has been explored to create complex ceramic structures, but current techniques face a tradeoff between precisely controlled feature sizes and high shrinkage at the microscales. Here, we introduce 3D-AJP, a novel freeform ceramic fabrication method that enables highly complex microscale 3D ceramic architectures-such as micropillars, spirals, and lattices-with minimal shrinkage and no auxiliary support. Using a near-binder-free nanoparticle ink in an Aerosol Jet (AJ) 3D printer, our approach precisely controls feature sizes down to 20 µm with aspect ratios up to 30:1. The resulting structures exhibit exceptionally low linear shrinkage of 2-6% upon sintering, spanning five orders of magnitude in length scale. Bi-material 3D architectures (zinc oxide/zirconia, zinc oxide/titania, titania/zirconia) and hybrid ceramics further demonstrate the technique's versatility. We showcase two key applications. First, 3D ceramic photocatalysts improve water purification performance, achieving a 400% increase in photocatalytic efficiency compared to bulk ceramics. Second, we develop a highly sensitive Her2 biomarker sensor for breast cancer detection, achieving a 22-second response time and a record-low detection limit of 0.0193 fm. Our technique will lead to high-performance sensing, filtration, microelectronics packaging, catalysis, and tissue regeneration technologies.

Recent Advances in 3D Printed Electrodes - Bridging the Nano to Mesoscale

3D architected electrodes offer inherent physicochemical advantages for energy storage, conversion, and sensing. 3D printing methods such as stereolithography and two photon polymerization are uniquely capable of fabricating these architected electrodes with a high degree of geometric complexity impossible to achieve with other methods at the mesoscale (10 µm-1 mm). The material set for 3D printing traditionally is focused on structural materials rather than functional materials suitable for electronic and electrochemical applications. In this review the fundamental challenges are considered for transforming 3D printed materials into conductive, multifunctional electrodes suitable for electrical and electrochemical devices by printing nanocomposites, infusing molecular precursors and post-processing these structures via carbonization. To understand the design of 3D electrodes toward their use in both sensors and electrochemical devices such as catalysts, this review summarizes recent advances in hierarchical design of porous metastructures, the engineering of mass transport and electronic transport in 3D structures, and the application of high-throughput materials design by machine learning and artificial intelligence. These emerging approaches to 3D electrode design and architecture promise to expand the capabilities of additive manufacturing beyond structural materials and bring its advantages to bear on modern devices such as sensors, batteries, supercapacitors, and electrocatalysts.

Attomolar-sensitive milk fever sensor using 3D-printed multiplex sensing structures

The diagnosis of milk fever or hypocalcemia in lactating cows has a significant economic impact on the dairy industry. It is challenging to identify asymptomatic subclinical hypocalcemia (SCH) in transition dairy cows. Monitoring subclinical hypocalcemia in milk samples can expedite treatment and improve the health, productivity, and welfare of dairy cows. In this study, an attomolar-sensitive sensor is developed using extrusion-based 3D-printed sensing structures to detect the ratio of ionized calcium to phosphate levels in milk samples. The unique geometries of the lateral structure of 3D-printed sensors, along with the wrinkled surfaces, provide a limit of detection down to the attomole (138 aM) concentration of the target analyte. The calcium-to-phosphate ratio in milk samples not only provides early disease indications but also enables on-site testing. This highly selective test is validated using real milk and blood samples, and the results are compared with those of commercial meters. This fast response (~10 s) low-cost sensor opens a promising tool for the farm-side diagnostic of dairy cows that can promote best practice management of dairy cows.

Electrochemical Detection of Nucleic Acids Using Three-Dimensional Graphene Screen-Printed Electrodes

Electrochemical approaches, along with miniaturization of electrodes, are increasingly being employed to detect and quantify nucleic acid biomarkers. Miniaturization of the electrodes is achieved through the use of screen-printed electrodes (SPEs), which consist of one to a few dozen sets of electrodes, or by utilizing printed circuit boards. Electrode materials used in SPEs include glassy carbon (Chiang H-C, Wang Y, Zhang Q, Levon K, Biosensors (Basel) 9:2-11, 2019), platinum, carbon, and graphene (Cheng FF, He TT, Miao HT, Shi JJ, Jiang LP, Zhu JJ, ACS Appl Mater Interfaces 7:2979-2985, 2015). There are numerous modifications to the electrode surfaces as well (Cheng FF, He TT, Miao HT, Shi JJ, Jiang LP, Zhu JJ, ACS Appl Mater Interfaces 7:2979-2985, 2015). These approaches offer distinct advantages, primarily due to their demonstrated superior limit of detection without amplification. Using the SPEs and potentiostats, we can detect cells, proteins, DNA, and RNA concentrations in the nanomolar (nM) to attomolar (aM) range. The focus of this chapter is to describe the basic approach adopted for the use of SPEs for nucleic acid measurement.

Cilia-Inspired Bionic Tactile E-Skin: Structure, Fabrication and Applications

The rapid advancement of tactile electronic skin (E-skin) has highlighted the effectiveness of incorporating bionic, force-sensitive microstructures in order to enhance sensing performance. Among these, cilia-like microstructures with high aspect ratios, whose inspiration is mammalian hair and the lateral line system of fish, have attracted significant attention for their unique ability to enable E-skin to detect weak signals, even in extreme conditions. Herein, this review critically examines recent progress in the development of cilia-inspired bionic tactile E-skin, with a focus on columnar, conical and filiform microstructures, as well as their fabrication strategies, including template-based and template-free methods. The relationship between sensing performance and fabrication approaches is thoroughly analyzed, offering a framework for optimizing sensitivity and resilience. We also explore the applications of these systems across various fields, such as medical diagnostics, motion detection, human-machine interfaces, dexterous robotics, near-field communication, and perceptual decoupling systems. Finally, we provide insights into the pathways toward industrializing cilia-inspired bionic tactile E-skin, aiming to drive innovation and unlock the technology's potential for future applications.

Numerical Investigation of a Microfluidic Biosensor Based on I-Shaped Micropillar Array Electrodes

Micropillar array electrodes offer several advantages, such as enhanced mass transport, lower detection limits, and the potential for miniaturization, making them instrumental in the design and fabrication of electrochemical biosensors. The performance of these biosensors is influenced by electrode geometry, including parameters like shape and height, which affect surface area and overall sensitivity. In this study, we designed a microfluidic electrochemical biosensor featuring micropillar array electrodes, modeled in COMSOL Multiphysics. We compared the response currents of I-shaped and cylindrical micropillar array electrodes. The working electrode (WE), consisting of 100 micropillars with a height of 300 µm, exhibited a sensitivity of 1.61 µA·cm2·mM-1 in cyclic voltammetry, highlighting its effectiveness for analyte detection.

General In Situ Engineering of Carbon-Based Materials on Carbon Fiber for In Vivo Neurochemical Sensing

Developing real-time, dynamic, and in situ analytical methods with high spatial and temporal resolutions is crucial for exploring biochemical processes in the brain. Although in vivo electrochemical methods based on carbon fiber (CF) microelectrodes are effective in monitoring neurochemical dynamics during physiological and pathological processes, complex post modification hinders large-scale productions and widespread neuroscience applications. Herein, we develop a general strategy for the in situ engineering of carbon-based materials to mass-produce functional CFs by introducing polydopamine to anchor zeolitic imidazolate frameworks as precursors, followed by one-step pyrolysis. This strategy demonstrates exceptional universality and design flexibility, overcoming complex post-modification procedures and avoiding the delamination of the modification layer. This simplifies the fabrication and integration of functional CF-based microelectrodes. Moreover, we design highly stable and selective H+, O2, and ascorbate microsensors and monitor the influence of CO2 exposure on the O2 content of the cerebral tissue during physiological and ischemia-reperfusion pathological processes.

3D Porous Graphene Architecture Integrated with Cu2O for Enhanced Electrochemical Sensing Performance

Construction and functionalization of a 3D graphene architecture are crucial to harness and extend the unique features of graphene and thus essential for its numerous conventional and novel applications. Herein, a 3D honeycomb-patterned porous graphene architecture is constructed through a facile and low-cost self-assembly process and then integrated with Cu2O nanoparticles via a simple electrodeposition procedure. The 3D porous graphene structure is prepared by the breath figure method using a graphene oxide (GO)-based complex in which GO is modified by a surfactant as the casting material. Benefiting from the intercalation of the surfactant between the GO nanosheets and the fabrication of a 3D porous structure, the aggregation inhibition of GO nanosheets and increases in accessible surface area are realized at both nano- and microscales, resulting in good electrochemical performance. Moreover, the deposition of Cu2O nanoparticles can further improve the electrochemical sensing performance of the porous reduced graphene oxide (rGO) structure. Extremely low detection limit (30.72 nM) with a linear range of 0 μM to 30 μM, excellent anti-interference, repeatability, reproducibility, stability, and high accuracy for actual sample testing are shown when the 3D porous Cu2O/rGO film is applied as an electrochemical sensor for DA detection. This work provides not only a superior electrochemical biosensor but also a simple, yet effective and general strategy for the construction and functionalization of a 3D graphene structure.

Enhanced aerosol-jet printing using annular acoustic field for high resolution and minimal overspray

Aerosol jet printing has the potential to fabricate fine features on various substrates due to its large stand-off distance. However, the presence of overspray and instability, particularly at high printing resolutions, has limited its widespread application. In this study, we introduce an efficient approach called annular acoustic focusing for aerosol jet printing. By determining the optimal focusing frequency (5.8 MHz) for silver nanoparticles using a particle ejection model, we achieve precise and stable printing. We also propose a modified print nozzle geometry, resulting in ultrafine traces (line width < 6 μm, overspray < 0.1 μm). Compared to printing without acoustic focusing, the line width of the traces decreases to 60 ± 5% while their conductivity increases to 180 ± 5%. Additionally, several 8 h experiments demonstrate excellent printing stability. This research opens up possibilities for the fabrication of conformal electronics with high precision and improved conductivity using aerosol jet printing.

Ultrasensitive Monolithic Dopamine Microsensors Employing Vertically Aligned Carbon Nanofibers

Brain-on-Chip devices, which facilitate on-chip cultures of neurons to simulate brain functions, are receiving tremendous attention from both fundamental and clinical research. Consequently, microsensors are being developed to accomplish real-time monitoring of neurotransmitters, which are the benchmarks for neuron network operation. Among these, electrochemical sensors have emerged as promising candidates for detecting a critical neurotransmitter, dopamine. However, current state-of-the-art electrochemical dopamine sensors are suffering from issues like limited sensitivity and cumbersome fabrication. Here, a novel route in monolithically microfabricating vertically aligned carbon nanofiber electrochemical dopamine microsensors is reported with an anti-blistering slow cooling process. Thanks to the microfabrication process, microsensors is created with complete insulation and large surface areas. The champion device shows extremely high sensitivity of 4.52× 104 µAµM-1·cm-2, which is two-orders-of-magnitude higher than current devices, and a highly competitive limit of detection of 0.243 nM. These remarkable figures-of-merit will open new windows for applications such as electrochemical recording from a single neuron.

Electrochemical and Plasmonic Detection of Myocardial Infarction Using Microfluidic Biochip Incorporated with Mesoporous Nanoscaffolds

This paper reports a microfluidic device for the electrochemical and plasmonic detection of cardiac myoglobin (cMb) and cardiac troponin I (cTnI) with noticeable limits of detection (LoD) as low as a few picograms per milliliter (pg/mL) ranges, achieved in a short detection time. The device features two working electrodes, each with a mesoporous Ni3V2O8 nanoscaffold grafted with reduced graphene oxide (rGO) that improves the interaction of diffusing analyte molecules with the sensing surface by providing a high surface area and reaction kinetics. Electrochemical studies reveal sensitivities as high as 9.68 μA ng/mL and a LoD of 2.0 pg/mL for cTnI, and 8.98 μA ng/mL and 4.7 pg/mL for cMb. Additionally, the surface plasmon resonance (SPR) studies demonstrate a low-level LoD of 8.8 pg/mL for cMb and 7.3 pg/mL for cTnI. The dual-modality sensor enables dynamic tracking of kinetic antigen-antibody interactions during sensing, self-verification through providing signals of two modes, and reduced false readout. This study demonstrates the complementary nature of the electrochemical and SPR modes in biosensing, with the electrochemical mode being highly sensitive and the SPR mode providing superior tracking of molecular recognition behaviors. The presented sensor represents a significant innovation in cardiovascular disease management and can be applied to monitor other clinically important biomolecules.

Structure-Switching Electrochemical Aptasensor for Rapid, Reagentless, and Single-Step Nanomolar Detection of C-Reactive Protein

C-reactive protein (CRP) is an acute-phase reactant and sensitive indicator for sepsis and other life-threatening pathologies, including systemic inflammatory response syndrome. Currently, clinical turn-around times for established CRP detection methods take between 30 min to hours or even days from centralized laboratories. Here, we report the development of an electrochemical biosensor using redox probe-tagged DNA aptamers, functionalized onto inexpensive, commercially available screen-printed electrodes. Binding-induced conformational switching of the CRP-targeting aptamer induces a specific and selective signal-ON event, which enables single-step and reagentless detection of CRP in as little as 1 min. The aptasensor limit of detection spans approximately 20-60 nM in 50% human serum with dynamic response windows spanning 1-200 or 1-500 nM (R = 0.97/R = 0.98 respectively). The sensor is stable for at least 1 week and can be reused numerous times, as judged from repeated real-time dosing and dose-response assays. By decoupling binding events from the signal induction mechanism, structure-switching electrochemical aptamer-based sensors provide considerable advantages over their adsorption-based counterparts. Our work expands on the retinue of such sensors reported in the literature and is the first instance of structure-switching electrochemical aptamer-based sensors (SS-EABs) for reagentless, voltammetric CRP detection. We hope this study inspires further investigations into the suitability of SS-EABs for diagnostics, which will aid translational R&D toward fully realized devices aimed at point-of-care applications or for broader use by the public.

Recent Advances in Tactile Sensory Systems: Mechanisms, Fabrication, and Applications

Flexible electronics is a cutting-edge field that has paved the way for artificial tactile systems that mimic biological functions of sensing mechanical stimuli. These systems have an immense potential to enhance human-machine interactions (HMIs). However, tactile sensing still faces formidable challenges in delivering precise and nuanced feedback, such as achieving a high sensitivity to emulate human touch, coping with environmental variability, and devising algorithms that can effectively interpret tactile data for meaningful interactions in diverse contexts. In this review, we summarize the recent advances of tactile sensory systems, such as piezoresistive, capacitive, piezoelectric, and triboelectric tactile sensors. We also review the state-of-the-art fabrication techniques for artificial tactile sensors. Next, we focus on the potential applications of HMIs, such as intelligent robotics, wearable devices, prosthetics, and medical healthcare. Finally, we conclude with the challenges and future development trends of tactile sensors.

Multijet Gold Nanoparticle Inks for Additive Manufacturing of Printed and Wearable Electronics

Conductive and biofriendly gold nanomaterial inks are highly desirable for printed electronics, biosensors, wearable electronics, and electrochemical sensor applications. Here, we demonstrate the scalable synthesis of stable gold nanoparticle inks with low-temperature sintering using simple chemical processing steps. Multiprinter compatible aqueous gold nanomaterial inks were formulated, achieving resistivity as low as ∼10-6 Ω m for 400 nm thick films sintered at 250 °C. Printed lines with a resolution of <20 μm and minimal overspray were obtained using an aerosol jet printer. The resistivity of the printed patterns reached ∼9.59 ± 1.2 × 10-8 Ω m after sintering at 400 °C for 45 min. Our aqueous-formulated gold nanomaterial inks are also compatible with inkjet printing, extending the design space and manufacturability of printed and flexible electronics where metal work functions and chemically inert films are important for device applications.

Tip-Enhanced Sub-Femtomolar Steroid Immunosensing via Micropyramidal Flexible Conducting Polymer Electrodes for At-Home Monitoring of Salivary Sex Hormones

Noninvasive testing and continuous monitoring of ultralow-concentration hormones in biofluids have attracted increasing interest for health management and personalized medicine, in which saliva could fulfill the demand. Steroid sex hormones such as progesterone (P4) and β-estradiol (E2) are crucial for female wellness and reproduction; however, their concentrations in saliva can vary down to sub-pM and constantly fluctuate over several orders of magnitude. This remains a major obstacle toward user-friendly and reliable monitoring at home with low-cost flexible biosensors. Herein we introduce a 3D micropyramidal electrode architecture to address such challenges and achieve an ultrasensitive flexible electrochemical immunosensor with sub-fM-level detection capability of salivary sex hormones within a few minutes. This is enabled by micropyramidal electrode arrays consisting of a poly(3,4-ethylenedioxythiophene):poly(4-styrenesulfonate) (PEDOT:PSS) thin film as the coating layer and electrochemically decorated gold nanoparticles (AuNPs) to improve the antibody immobilization. The enhanced mass transport around the 3D tips provided by the micropyramidal architecture is discovered to improve the detection limit by 3 orders of magnitude, pushing it to as low as ∼100 aM for P4 and ∼20 aM for E2, along with a wide linear range up to μM. Accordingly, these hormones down to sub-fM in >1000-fold-diluted saliva samples can be accurately measured by the printed soft immunosensors, thus allowing at-home testing through simple saliva dilution to minimize the interfering substances instead of centrifugation. Finally, monitoring of the female ovarian hormone cycle of both P4 and E2 is successfully demonstrated based on the centrifuge-free saliva testing during a period of 4 weeks. This ultrasensitive and soft 3D microarchitected electrode design is believed to provide a universal platform for a diverse variety of applications spanning from accurate clinical diagnostics and counselling and in vivo detection of bioactive species to environmental and food quality tracing.

3D Printing for Cancer Diagnosis: What Unique Advantages Are Gained?

Cancer is a complex disease with global significance, necessitating continuous advancements in diagnostics and treatment. 3D printing technology has emerged as a revolutionary tool in cancer diagnostics, offering immense potential in detection and monitoring. Traditional diagnostic methods have limitations in providing molecular and genetic tumor information that is crucial for personalized treatment decisions. Biomarkers have become invaluable in cancer diagnostics, but their detection often requires specialized facilities and resources. 3D printing technology enables the fabrication of customized sensor arrays, enhancing the detection of multiple biomarkers specific to different types of cancer. These 3D-printed arrays offer improved sensitivity, allowing the detection of low levels of biomarkers, even in complex samples. Moreover, their specificity can be fine-tuned, reducing false-positive and false-negative results. The streamlined and cost-effective fabrication process of 3D printing makes these sensor arrays accessible, potentially improving cancer diagnostics on a global scale. By harnessing 3D printing, researchers and clinicians can enhance early detection, monitor treatment response, and improve patient outcomes. The integration of 3D printing in cancer diagnostics holds significant promise for the future of personalized cancer care.

The chloroperoxidase immobilized on porous carbon nanobowls for the detection of trichloroacetic acid by electroenzymatic synergistic catalysis

Trichloroacetic acid (TCA), as a by-product of chlorination disinfection, is a highly carcinogenic chemical. Due to the widespread use of chlorination disinfection, it is critical to detect TCA in drinking water to decrease the incidence of disease. In this work, we developed an efficient TCA biosensor via electroenzymatic synergistic catalysis. The porous carbon nanobowls (PCNB) are prepared and wrapped by an amyloid like proteins formed by phase-transitioned lysozyme (PTL-PCNB), then, chloroperoxidase (CPO) is abounding to PTL-PCNB owing to its strong adhesion. The ionic liquid of 1-ethyl-3-methylimidazolium bromide (ILEMB) is co-immobilized on PTL-PCNB to from CPO-ILEMB@PTL-PCNB nanocomposite to assist the direct electron transfer (DET) of CPO. The PCNB plays two roles here. In addition, to increasing the conductivity, it serves as an ideal support for holding CPO; The CPO-ILEMB@PTL-PCNB nanocomposite modified electrode presents high efficiency for sensing TCA. Through electroenzymatic synergistic catalysis, a wide detection range of 33 μmol L-1 to 98 mmol L-1 can be achieved with a low detection limit of 5.9 μmol L-1, and high stability, selectivity as well as reproducibility, which ensures its potential practical applicability. This work provides a new platform for the electro-enzyme synergistic catalysis in one pot.

Beyond Tissue replacement: The Emerging role of smart implants in healthcare

Smart implants are increasingly used to treat various diseases, track patient status, and restore tissue and organ function. These devices support internal organs, actively stimulate nerves, and monitor essential functions. With continuous monitoring or stimulation, patient observation quality and subsequent treatment can be improved. Additionally, using biodegradable and entirely excreted implant materials eliminates the need for surgical removal, providing a patient-friendly solution. In this review, we classify smart implants and discuss the latest prototypes, materials, and technologies employed in their creation. Our focus lies in exploring medical devices beyond replacing an organ or tissue and incorporating new functionality through sensors and electronic circuits. We also examine the advantages, opportunities, and challenges of creating implantable devices that preserve all critical functions. By presenting an in-depth overview of the current state-of-the-art smart implants, we shed light on persistent issues and limitations while discussing potential avenues for future advancements in materials used for these devices.

All-Carbon Solution-Gated Transistor with Low Operating Voltages for Highly Selective and Stable Dopamine Sensing

The diversity of carbon materials makes it possible to prepare all-carbon electronic devices requiring components with different properties and functions. In this work, we fabricate an all-carbon solution-gated transistor (AC-SGT) based dopamine (DA) sensor with Nafion coated nitrogen and oxygen co-doped carbon yarn (Nafion/NOCY) as the gate electrode and graphene as the channel. The carbon materials in AC-SGT render the usage of a variety of strategies to improve its electrochemical sensing capability including the modification of the gate electrode and the modulation of the operating voltage. With a low gate-source voltage of 0.02 V as well as a low drain-source voltage of 0.05 V, AC-SGT manifests the outstanding DA sensing performances in terms of sensitivity, selectivity, limit of detection (3 nM, S/N > 3), linear range (3 nM to 300 μM), long-term stability (over 30 days), and preconditioning time (60 s). Furthermore, a smartphone controlled portable sensing system integrated with AC-SGT is fabricated herein, which shows the excellent in vitro sensing capability of DA in urine, proving the potential of all-carbon transistors in smart wearable biosensors.

Wearable chemical sensors based on 2D materials for healthcare applications

Chemical sensors worn on the body could make possible the continuous, noninvasive, and accurate monitoring of vital human signals, which is necessary for remote health monitoring and telemedicine. Attractive for creating high-performance, wearable chemical sensors are atomically thin materials with intriguing physical features, abundant chemistry, and high surface-to-volume ratios. These advantages allow for appropriate material-analyte interactions, resulting in a high level of sensitivity even at trace analyte concentrations. Previous review articles covered the material and device elements of 2D material-based wearable devices extensively. In contrast, little research has addressed the existing state, future outlook, and promise of 2D materials for wearable chemical sensors. We provide an overview of recent advances in 2D-material-based wearable chemical sensors to overcome this deficiency. The structure design, manufacturing techniques, and mechanisms of 2D material-based wearable chemical sensors will be evaluated, as well as their applicability in human health monitoring. Importantly, we present a thorough review of the current state of the art and the technological gaps that would enable the future design and nanomanufacturing of 2D materials and wearable chemical sensors. Finally, we explore the challenges and opportunities associated with designing and implementing 2D wearable chemical sensors.

Ultrasensitive dopamine detection with graphene aptasensor multitransistor arrays

Detecting physiological levels of neurotransmitters in biological samples can advance our understanding of brain disorders and lead to improved diagnostics and therapeutics. However, neurotransmitter sensors for real-world applications must reliably detect low concentrations of target analytes from small volume working samples. Herein, a platform for robust and ultrasensitive detection of dopamine, an essential neurotransmitter that underlies several brain disorders, based on graphene multitransistor arrays (gMTAs) functionalized with a selective DNA aptamer is presented. High-yield scalable methodologies optimized at the wafer level were employed to integrate multiple graphene transistors on small-size chips (4.5 × 4.5 mm). The multiple sensor array configuration permits independent and simultaneous replicate measurements of the same sample that produce robust average data, reducing sources of measurement variability. This procedure allowed sensitive and reproducible dopamine detection in ultra-low concentrations from small volume samples across physiological buffers and high ionic strength complex biological samples. The obtained limit-of-detection was 1 aM (10–18) with dynamic detection ranges spanning 10 orders of magnitude up to 100 µM (10–8), and a 22 mV/decade peak sensitivity in artificial cerebral spinal fluid. Dopamine detection in dopamine-depleted brain homogenates spiked with dopamine was also possible with a LOD of 1 aM, overcoming sensitivity losses typically observed in ion-sensitive sensors in complex biological samples. Furthermore, we show that our gMTAs platform can detect minimal changes in dopamine concentrations in small working volume samples (2 µL) of cerebral spinal fluid samples obtained from a mouse model of Parkinson’s Disease. The platform presented in this work can lead the way to graphene-based neurotransmitter sensors suitable for real-world academic and pre-clinical pharmaceutical research as well as clinical diagnosis.

N protein-based ultrasensitive SARS-CoV-2 antibody detection in seconds via 3D nanoprinted, microarchitected array electrodes

Rapid detection of antibodies to SARS-CoV-2 is critical for COVID-19 diagnostics, epidemiological research, and studies related to vaccine evaluation. It is known that the nucleocapsid (N) is the most abundant protein of SARS-CoV-2 and can serve as an excellent biomarker due to its strong immunogenicity. This paper reports a rapid and ultrasensitive 3D biosensor for quantification of COVID-19 antibodies in seconds via electrochemical transduction. This sensor consists of an array of three-dimensional micro-length-scale electrode architecture that is fabricated by aerosol jet 3D printing, which is an additive manufacturing technique. The micropillar array is coated with N proteins via an intermediate layer of nano-graphene and is integrated into a microfluidic channel to complete an electrochemical cell that uses antibody-antigen interaction to detect the antibodies to the N protein. Due to the structural innovation in the electrode geometry, the sensing is achieved in seconds, and the sensor shows an excellent limit of detection of 13 fm and an optimal detection range of 100 fm to 1 nm. Furthermore, the sensor can be regenerated at least 10 times, which reduces the cost per test. This work provides a powerful platform for rapid screening of antibodies to SARS-CoV-2 after infection or vaccination.

Recent Advances in 3D Printing of Biomedical Sensing Devices

Additive manufacturing, also called 3D printing, is a rapidly evolving technique that allows for the fabrication of functional materials with complex architectures, controlled microstructures, and material combinations. This capability has influenced the field of biomedical sensing devices by enabling the trends of device miniaturization, customization, and elasticity (i.e., having mechanical properties that match with the biological tissue). In this paper, the current state-of-the-art knowledge of biomedical sensors with the unique and unusual properties enabled by 3D printing is reviewed. The review encompasses clinically important areas involving the quantification of biomarkers (neurotransmitters, metabolites, and proteins), soft and implantable sensors, microfluidic biosensors, and wearable haptic sensors. In addition, the rapid sensing of pathogens and pathogen biomarkers enabled by 3D printing, an area of significant interest considering the recent worldwide pandemic caused by the novel coronavirus, is also discussed. It is also described how 3D printing enables critical sensor advantages including lower limit-of-detection, sensitivity, greater sensing range, and the ability for point-of-care diagnostics. Further, manufacturing itself benefits from 3D printing via rapid prototyping, improved resolution, and lower cost. This review provides researchers in academia and industry a comprehensive summary of the novel possibilities opened by the progress in 3D printing technology for a variety of biomedical applications.