Fabrication of Aptamer-Modified Paper Electrochemical Devices for On-Site Biosensing

Cold-hot Janus electrochemical aptamer-based sensor for calibration-free determination of biomolecules

Real-time, high-frequency measurements of pharmaceuticals, metabolites, exogenous antigens, and other biomolecules in biological samples can provide critical information for health management and clinical diagnosis. Electrochemical aptamer-based (EAB) sensor is a promising analytical technique capable of achieving these goals. However, the issues of insufficient sensitivity, frequent calibration and lack of adapted portable electrochemical device limit its practical application in immediate detection. In response we have fabricated an on-chip-integrated, cold-hot Janus EAB (J-EAB) sensor based on the thermoelectric coolers (TECs). Attributed to the Peltier effect, the enhanced/suppressed current response can be generated simultaneously on cold/hot sides of the J-EAB sensor. The ratio of the current responses on the cold and hot sides was used as the detection signal, enabling rapid on-site, calibration-free determination of small molecules (procaine) as well as macromolecules (SARS-CoV-2 spike protein) in single step, with detection limits of 1 μM and 10 nM, respectively. We have further demonstrated that the J-EAB sensor is effective in improving the ease and usability of the actual detection process, and is expected to provide a universal, low-cost, fast and easy potential analytical tool for other clinically important biomarkers, drugs or pharmaceutical small molecules.

Portable dual-mode paper chips for highly sensitive and rapid determination of aflatoxin B1 via an aptamer-gated MOFs

Paper chip as a representative microfluidic device has been mushroomed for rapid identification of contaminants in agro-food. However, the sensitivity and accuracy have still been challenged by inevitable background noise or interference in food matrix. Herein, we designed and fabricated a dual-mode paper chip (DPC) by assembling a patterned paper electrode with a platinum nanoparticles-treated colorimetric region through a flow channel. Dual-mode outputs were guided by an aptamer-gated UiO-66-NH2 metal-organic frameworks (MOFs). UiO-66-NH2 loaded with 3, 3', 5, 5'-tetramethylbenzidine (TMB) was controlled by a switch comprised of CdS quantum dots-aptamer. Aflatoxin B1 (AFB1, a kind of carcinogenic mycotoxin) target came and induced TMB release, triggering colorimetric and ECL signals on DPC, ultra-high sensitivity with a detection limit of 7.8 fg/mL was realized. The practicability of the DPC was also confirmed by spiking AFB1 in real corn samples. This portable paper-based device provides an ideal rapid detection platform tailored for diverse food contaminants analysis.

Rapid nanomolar detection of cocaine in biofluids by electrochemical aptamer-based sensor with low-temperature effect for drugged driving screening

Cocaine is one of the most abused illicit drugs, and its abuse damages the central nervous system and can even lead directly to death. Therefore, the development of simple, rapid and highly sensitive detection methods is crucial for the prevention and control of drug abuse, traffic accidents and crime. In this work, an electrochemical aptamer-based (EAB) sensor based on the low-temperature enhancement effect was developed for the direct determination of cocaine in bio-samples. The signal gain of the sensor at 10 °C was greatly improved compared to room temperature, owing to the improved affinity between the aptamer and the target. Additionally, the electroactive area of the gold electrode used to fabricate the EAB sensor was increased 20 times by a simple electrochemical roughening method. The porous electrode possesses more efficient electron transfer and better antifouling properties after roughening. These improvements enabled the sensor to achieve rapid detection of cocaine in complex bio-samples. The low detection limits (LOD) of cocaine in undiluted urine, 50% serum and 50% saliva were 70 nM, 30 nM and 10 nM, respectively, which are below the concentration threshold in drugged driving screening. The aptasensor was simple to construct and reusable, which offers potential for drugged driving screening in the real world.

CRISPR/Cas12a integrated electrochemiluminescence biosensor for pufferfish authenticity detection based on NiCo2O4 NCs@Au as a coreaction accelerator

Meat adulteration has brought economic losses, health risks, and religious concerns, making it a pressing global issue. Herein, combining the high amplification efficiency of polymerase chain reaction (PCR) and the accurate recognition of CRISPR/Cas12, a sensitive and reliable electrochemiluminescence (ECL) biosensor was developed for the detection of pufferfish authenticity using NiCo2O4 NCs@Au-ABEI as nanoemitters. In the presence of target DNA, the trans-cleavage activity of CRISPR/Cas12a is activated upon specific recognition by crRNA, and then it cleaves dopamine-modified single stranded DNA (ssDNA-DA), triggering the ECL signal from the "off" to "on" state. However, without target DNA, the trans-cleavage activity of CRISPR/Cas12a is silenced. By rationally designing corresponding primers and crRNA, the biosensor was applied to specific identification of four species of pufferfish. Furthermore, as low as 0.1 % (w/w) adulterate pufferfish in mixture samples could be detected. Overall, this work provides a simple, low-cost and sensitive approach to trace pufferfish adulteration.

Aptamer-modified paper-based analytical devices for the detection of food hazards: Emerging applications and future perspective

Food analysis plays a critical role in assessing human health risks and monitoring food quality and safety. Currently, there is a pressing need for a reliable, portable, and quick recognition element for point-of-care testing (POCT) to better serve the demands of on-site food analysis. Aptamer-modified paper-based analytical devices (Apt-PADs) have excellent characteristics of high portability, high sensitivity, high specificity, and on-site detection, which have been widely used and concerned in the field of food safety. The article reviews the basic components and working principles of Apt-PADs, and introduces their representative applications detecting food hazards. Finally, the advantages, challenges, and future directions of Apt-PADs-based sensing performance are discussed, to provide new directions and insights for researchers to select appropriate Apt-PADs according to specific applications.

Aptamer-based diagnostic and therapeutic approaches for animal viruses: A review

Animal diseases often have significant consequences due to the unclear and time-consuming diagnosis process. Furthermore, the emergence of new viral infections and drug-resistant pathogens has further complicated the diagnosis and treatment of viral diseases. Aptamers, which are obtained through systematic evolution of ligands by exponential enrichment (SELEX) technology, provide a promising solution as they enable specific identification and binding to targets, facilitating pathogen detection and the development of novel therapeutics. This review presented an overview of aptasensors for animal virus detection, discussed the antiviral activity and mechanisms of aptamers, and highlighted advancements in aptamer-based antiviral research following the COVID-19 pandemic. Additionally, the challenges and prospects of aptamer-based virus diagnosis and treatment research were explored. Although this review was not exhaustive, it offered valuable insights into the progress of aptamer-based antiviral drug research, target mechanisms, as well as the development of novel antiviral drugs and biosensors.

CRISPR/Cas12a-Derived Photoelectrochemical Aptasensor Based on Au Nanoparticle-Attached CdS/UiO-66-NH2 Heterostructures for the Rapid and Sensitive Detection of Ochratoxin A

The sensitive and accurate detection of ochratoxin A (OTA) is crucial for public health due to its high toxicity. Herein, using Au nanoparticle (NP)-attached CdS/UiO-66-NH2 heterostructures as photoactive materials, a photoelectrochemical (PEC) aptasensor was presented for the ultrasensitive assay of OTA based on a competitive displacement reaction triggering the trans-cleavage ability of CRISPR/Cas12a. In this sensing strategy, methylene blue-labeled single-stranded DNA (MB-ssDNA) was immobilized on the Au NPs/CdS/UiO-66-NH2 electrode to accelerate the separation of the photogenerated carrier, thus producing a significantly increased PEC response. In the presence of OTA, it specifically bound with the aptamer (Apt) and resulted in the release of the activation chain, triggering the trans-cleavage characteristics of CRISPR/Cas12a. MB-ssDNA was cut randomly on the electrode surface to convert the PEC signal from the "on" to the "off" state, thereby achieving a quantitative and accurate detection of OTA. The CRISPR/Cas12a-derived PEC aptasensor exhibited excellent sensitivity and specificity, with a linear range from 100 to 50 ng/mL and a detection limit of 38 fg/mL. Overall, the proposed aptasensor could provide a rapid, accurate, and sensitive method for the determination of OTA in actual samples.

Phospholipid Bilayer Integrated with Multifunctional Peptide for Ultralow-Fouling Electrochemical Detection of HER2 in Human Serum

Electrochemical biosensing devices face challenges of severe nonspecific adsorption in complex biological matrices for the detection of biomarkers, and thus, there is a significant need for sensitive and antifouling biosensors. Herein, a sensitive electrochemical biosensor with antifouling and antiprotease hydrolysis ability was constructed for the detection of human epidermal growth factor receptor 2 (HER2) by integrating multifunctional branched peptides with distearoylphosphatidylethanolamine-poly(ethylene glycol) (DSPE-PEG) self-assembled bilayer. The peptide was designed to possess antifouling, antiprotease hydrolysis, and HER2 recognizing capabilities. Molecular dynamics simulations demonstrated that the DSPE was able to effectively self-assemble into a bilayer, and the water contact angle and electrochemical experiments verified that the combination of peptide with the DSPE-PEG bilayer was conducive to enhancing the hydrophilicity and antifouling performance of the modified surface. The constructed HER2 biosensor exhibited excellent antifouling and antiprotease hydrolysis capabilities, and it possessed a linear range of 1.0 pg mL-1 to 1.0 μg mL-1, and a limit of detection of 0.24 pg mL-1. In addition, the biosensor was able to detect HER2 in real human serum samples without significant biofouling, and the assaying results were highly consistent with those measured by the enzyme-linked immunosorbent assay (ELISA), indicating the promising potential of the antifouling biosensor for clinical diagnosis.

Aptamer-Based Fentanyl Detection in Biological Fluids

Fentanyl is a widely abused analgesic and anesthetic drug with a narrow therapeutic window that creates easy opportunities for overdose and death. Rapid, accurate, and sensitive fentanyl detection in biosamples is crucial for therapeutic drug monitoring and overdose diagnosis. Unfortunately, current methods are limited to either sophisticated laboratory-based tests or antibody-based immunoassays, which are prone to false results and are mainly used with urine samples. Here, we have utilized library-immobilized SELEX to isolate new aptamers─nucleic acid-based bioreceptors that are well-suited for biosensing─that can specifically bind fentanyl under physiological conditions. We isolated multiple aptamers with nanomolar affinity and excellent specificity against dozens of interferents and incorporated one of these into an electrochemical aptamer-based sensor that can rapidly detect fentanyl at clinically relevant concentrations in 50% diluted serum, urine, and saliva. Given the excellent performance of these sensors, we believe that they could serve as the basis for point-of-care devices for monitoring fentanyl during medical procedures and determining fentanyl overdose.

Tetrahedral DNA Nanostructure-Engineered Paper-Based Electrochemical Aptasensor for Fumonisin B1 Detection Coupled with Au@Pt Nanocrystals as an Amplification Label

Fumonisin B1 (FB1), as one of the highest toxicity mycotoxins, poses a serious threat to animal and human health, even at low concentrations. It is significant and challenging to develop a sensitive and reliable analytical device. Herein, a paper-based electrochemical aptasensor was designed utilizing tetrahedral DNA nanostructures (TDNs) to controllably anchor an aptamer (Apt), improving the recognition efficiency of Apt to its target. First, gold nanoparticles (AuNPs)@MXenes were used as a sensing substrate with good conductivity and modified on the electrode for immobilization of complementary DNA-TDNs (cDNA-TDNs). In the absence of FB1, numerous Apt-Au@Pt nanocrystals (NCs) was hybridized with cDNA and assembled on the sensing interface, which accelerated the oxidation of TMB with H2O2 and produced a highly amplified differential pulse voltammetry (DPV) signal. When the target FB1 specifically bound to its Apt, the electrochemical signal was decreased by releasing the Apt-Au@Pt NCs from double-stranded DNA (dsDNA). On account of the strand displacement reaction by FB1 triggering, the aptasensor had a wider dynamic linear range (from 50 fg/mL to 100 ng/mL) with a lower limit of detection (21 fg/mL) under the optimized conditions. More impressively, the designed FB1 aptasensor exhibited satisfactory performance in corn and wheat samples. Therefore, the TDN-engineered sensing platform opens an effective approach for sensitive and accurate analysis of FB1, holding strong potential in food safety and public health.

Wearable electrochemical sensor based on bimetallic MOF coated CNT/PDMS film electrode via a dual-stamping method for real-time sweat glucose analysis

Non-invasive wearable sweat glucose sensors are expected to be highly desirable for personalized diabetes management. Therefore, developing facile, convenient, and scalable manufacturing method of such wearable sensors is urgently needed. Herein, we report a simple and low-cost stamping-vacuum filtration dry transfer (SVFDT) method for construction of a wearable sweat glucose electrochemical sensor. In this patch, a three-electrode array template was made by using a polyvinyl chloride (PVC) stamp, followed by the preparation of multiwalled carbon nanotubes (MWCNTs)/polydimethylsiloxane (PDMS) (MP) film electrode using the vacuum-filtration dry transfer method. In addition, for further enhancing the conductivity of the electrode, another similar stamp with a raised surface dipping carbon nanotubes (CNTs) conductive coating was stamped on the surface of the MP electrode to obtain CNTs/MWCNTs/PDMS (CMP) electrode. CMP electrode was modified with the enzyme-like Ni-Co metal-organic framework (MOF) material which showed good electro-catalytic activity and achieved high sensitivity for glucose detection with a low detection limit of 6.78 μM and a wide linear range of 20 μM - 1.1 mM. More importantly, the Ni-Co MOF modified CMP (NCMP) electrode also displayed high stability under stretching and bending conditions. Finally, the sweat absorbent cloth was combined with the NCMP film electrode to form a wearable flexible electrochemical sensor patch, which could adhere to the skin to enrich sweat and realize real-time detection of sweat glucose with high accuracy. This SVFDT method can also be applied to the fabrication of other electronic devices.

Flexible and Stretchable Organic Electrochemical Transistors for Physiological Sensing Devices

Flexible and stretchable bioelectronics provides a biocompatible interface between electronics and biological systems and has received tremendous attention for in situ monitoring of various biological systems. Considerable progress in organic electronics has made organic semiconductors, as well as other organic electronic materials, ideal candidates for developing wearable, implantable, and biocompatible electronic circuits due to their potential mechanical compliance and biocompatibility. Organic electrochemical transistors (OECTs), as an emerging class of organic electronic building blocks, exhibit significant advantages in biological sensing due to the ionic nature at the basis of the switching behavior, low driving voltage (<1 V), and high transconductance (in millisiemens range). During the past few years, significant progress in constructing flexible/stretchable OECTs (FSOECTs) for both biochemical and bioelectrical sensors has been reported. In this regard, to summarize major research accomplishments in this emerging field, this review first discusses structure and critical features of FSOECTs, including working principles, materials, and architectural engineering. Next, a wide spectrum of relevant physiological sensing applications, where FSOECTs are the key components, are summarized. Last, major challenges and opportunities for further advancing FSOECT physiological sensors are discussed.

Suite of Aptamer-Based Sensors for the Detection of Fentanyl and Its Analogues

Fentanyl and its analogues are potent synthetic opioids that are commonly abused and are currently the number one cause of drug overdose death in the United States. The ability to detect fentanyl with simple, rapid, and low-cost tools is crucial for forensics, medical care, and public safety. Conventional on-site testing options for fentanyl detection─including chemical spot tests, lateral-flow immunoassays, and portable Raman spectrometers─each have their own unique flaws that limit their analytical utility. Here, we have developed a series of new aptamer-based assays and sensors that can detect fentanyl as well as several of its analogues in a reliable, accurate, rapid, and economic manner. These include colorimetric, fluorescent, and electrochemical sensors, which can detect and quantify minute quantities of fentanyl and many of its analogues with no response to other illicit drugs, cutting agents, or adulterants─even in interferent-ridden binary mixtures containing as little as 1% fentanyl. Given the high performance of these novel analytical tools, we foresee the potential for routine use by medical and law enforcement personnel as well as the general public to aid in rapid and accurate fentanyl identification.

Development of Nafion/single-walled carbon nanotube integrated arrays for the rapid detection of salbutamol doping

Salbutamol (SAL), a drug originally intended for the treatment of bronchial and pulmonary diseases, has repeatedly been used for doping in competitive sports. Herein, an integrated array (NFCNT array) that prepared by template-assisted scalable filtration using Nafion-coated single-walled carbon nanotube (SWCNT) is presented for the rapid field detection of SAL. Spectroscopic and microscopic measurements were used to confirm the introduction of Nafion onto the surface of the array and to analyze the resulting morphological changes. The effects of Nafion addition on the resistance and electrochemical properties of the arrays (e.g., the electrochemically active area, charge-transfer resistance, and adsorption charge) are also discussed in depth. With an electrolyte/Nafion/SWCNT interface and moderate resistance, the NFCNT-4 array prepared containing 0.04 wt% Nafion suspension exhibits the greatest voltammetric response to SAL. Subsequently, a possible mechanism for the oxidation of SAL was proposed, and a calibration curve in the range of 0.1-15 μM was established. Finally, the NFCNT-4 arrays were applied to the detection of SAL in human urine samples with satisfactory recoveries.

Advances on microfluidic paper-based electroanalytical devices

Since the inception of the first electrochemical devices on paper substrates, many different reports of microfluidic paper-based electroanalytical devices (μPEDs), innovative hydrophobic barriers and electrode fabrication processes have allowed the incorporation of diverse materials, resulting in different applications and a boost in performance. These advancements have led to the creation of paper-based devices with comparable performance to many standard conventional devices, with the added benefits of pumpless fluidic transport, component separation and reagent storage that can be exploited to automate and handle sample preprocessing. Herein, we review μPEDs, summarize the characteristics and functionalities of μPEDs, such as separation, fluid flow control and storage, and outline the conventional and emerging fabrication and modification approaches for μPEDs. We also examine the recent application of μPEDs in biomedicine, the environment, and food and water safety, as well as some limitations and challenges that must be addressed.

Flexible Point-of-Care Electrodes for Ultrasensitive Detection of Bladder Tumor-Relevant miRNA in Urine

Portable point-of-care testing (POCT) is currently drawing enormous attention owing to its great potential for disease diagnosis and personal health management. Electrochemical biosensors, with the intrinsic advantages of cost-effectiveness, fast response, ease of miniaturization, and integration, are considered as one of the most promising candidates for POCT application. However, the clinical application of electrochemical biosensors-based POCT is hindered by the decreased detection sensitivity due to the low abundance of disease-relevant biomolecules in extremely complex biological samples. Herein, we construct a flexible electrochemical biosensor based on single-stranded DNA functionalized single-walled carbon nanotubes (ssDNA-SWNTs) for high sensitivity and stability detection of miRNA-21 in human urine to achieve bladder cancer (BCa) diagnosis and classification. The ssDNA-SWNT electrodes with a 2D interconnected network structure exhibit a high electrical conductivity, thus enabling the ultrasensitive detection of miRNA-21 with a detection limit of 3.0 fM. Additionally, the intrinsic flexibility of ssDNA-SWNT electrodes endows the biosensors with the capability to achieve high stability detection of miRNA-21 even under large bending deformations. In a cohort of 40 BCa patients at stages I-III and 44 negative control samples, the constructed ssDNA-SWNT biosensors could detect BCa with a 92.5% sensitivity, an 88.6% specificity, and classify the cancer stages with an overall accuracy of 81.0%. Additionally, the flexible ssDNA-SWNT biosensors could also be utilized for treatment efficiency assessment and cancer recurrence monitoring. Owing to their excellent sensitivity and stability, the designed flexible ssDNA-SWNT biosensors in this work propose a strategy to realize point-of-care detection of complex clinical samples to achieve personalized healthcare.

Paper-Based Bipolar Electrode Electrochemiluminescence Platform Combined with Pencil-Drawing Trace for the Detection of M.SssI Methyltransferase

Herein, a hand-drawing paper-based bipolar electrode (BPE) electrochemiluminescence (ECL) platform for M.SssI methyltransferase (M.SssI MTase) assay was proposed via employing high electrocatalytic Pt@CeO₂ as an ECL co-reaction accelerator and pencil-drawing graphite electric circuits as wires and electrodes. Notably, the introduction of pencil-drawing trace not only simplified the manufacturing process but also reduced the cost and saved fabricating time. Meanwhile, Pt@CeO₂ with good electrocatalytic activity and satisfactory chemical stability was used at the anode of the closed BPE-ECL device to accelerate the oxidation rate of uric acid. Due to the balanced charges of the bipolar electrode, the ECL response of the MnS: CdS@ZnS/S₂O₈^2- system emitted on the cathode was enhanced. In situ growth of gold nanoparticles in the two electrode areas was convenient for DNA immobilization. With the above points in mind, the specific DNA double strands functionalized via Pt@CeO₂ were employed to identify M.SssI MTase. The unmethylated DNA double strands were cut by HpaII endonuclease, resulting in the quenching of the ECL signal. Under the optimal conditions, sensitive detection of M.SssI MTase in a wide linear range of 0.01-100 U·mL^-1 with a satisfactory detection limit of 0.008 U·mL^-1 was realized. The reliable and versatile BPE-ECL tool for the determination of M.SssI MTase with easy-to-operate pencil-drawing traces and independent solution systems provides a new opportunity to develop paper-based devices applied in early disease diagnosis and pathogenesis research.

Wearable biosensors for human fatigue diagnosis: A review

Fatigue causes deleterious effects to physical and mental health of human being and may cause loss of lives. Therefore, the adverse effects of fatigue on individuals and the society are massive. With the ever-increasing frequency of overtraining among modern military and sports personnel, timely, portable and accurate fatigue diagnosis is essential to avoid fatigue-induced accidents. However, traditional detection methods require complex sample preparation and blood sampling processes, which cannot meet the timeliness and portability of fatigue diagnosis. With the development of flexible materials and biosensing technology, wearable biosensors have attracted increased attention to the researchers. Wearable biosensors collect biomarkers from noninvasive biofluids, such as sweat, saliva, and tears, followed by biosensing with the help of biosensing modules continuously and quantitatively. The detection signal can then be transmitted through wireless communication modules that constitute a method for real-time understanding of abnormality. Recent developments of wearable biosensors are focused on miniaturized wearable electrochemistry and optical biosensors for metabolites detection, of which, few have exhibited satisfactory results in medical diagnosis. However, detection performance limits the wide-range applicability of wearable fatigue diagnosis. In this article, the application of wearable biosensors in fatigue diagnosis has been discussed. In fact, exploration of the composition of different biofluids and their potential toward fatigue diagnosis have been discussed here for the very first time. Moreover, discussions regarding the current bottlenecks in wearable fatigue biosensors and the latest advancements in biochemical reaction and data communication modules have been incorporated herein. Finally, the main challenges and opportunities were discussed for wearable fatigue diagnosis in the future.

Recent Progress on Highly Selective and Sensitive Electrochemical Aptamer-based Sensors

Highly selective, sensitive, and stable biosensors are essential for the molecular level understanding of many physiological activities and diseases. Electrochemical aptamer-based (E-AB) sensor is an appealing platform for measurement in biological system, attributing to the combined advantages of high selectivity of the aptamer and high sensitivity of electrochemical analysis. This review summarizes the latest development of E-AB sensors, focuses on the modification strategies used in the fabrication of sensors and the sensing strategies for analytes of different sizes in biological system, and then looks forward to the challenges and prospects of the future development of electrochemical aptamer-based sensors.

Photosensitive-Stamp-Inspired Scalable Fabrication Strategy of Wearable Sensing Arrays for Noninvasive Real-Time Sweat Analysis

Wearable sweat sensing is essential to the development of personalized health monitoring in a noninvasive manner with molecular-level insight. Hence, there is an increasing demand for convenient, facile, and efficient fabrication of wearable sensing arrays. Inspired by a photosensitive stamp (PS), we present herein a simple, low-cost, and eco-friendly vacuum filtration-transfer printing method (termed PS-VFTP) for the scalable preparation of single-walled carbon nanotube (SWCNT) based flexible electrode arrays. This method can economically yield customized flexible SWCNT arrays with praiseworthy performance, such as high reproducibility, precision, uniformity, conductivity, and mechanical stability. In addition, the flexible SWCNT arrays can be easily functionalized into high-performance electrochemical sensors for the simultaneous monitoring of sweat metabolites (glucose, lactate) and electrolytes (Na⁺, K⁺). The integration of wearable sensing arrays with a signal acquisition and processing circuit system in the intelligent wearable sensors empowers them to realize noninvasive, real-time, and in situ sweat analysis during exercise. More meaningfully, such a PS-VFTP strategy can be easily expanded to the economical manufacturing of other flexible electronic devices.

CRISPR-Cas12a-mediated label-free electrochemical aptamer-based sensor for SARS-CoV-2 antigen detection

Serological antigen testing has emerged as an important diagnostic paradigm in COVID-19, but often suffers from potential cross-reactivity. To address this limitation, we herein report a label-free electrochemical aptamer-based sensor for the detection of SARS-CoV-2 antigen by integrating aptamer-based specific recognition with CRISPR-Cas12a-mediated signal amplification. The sensing principle is based on the competitive binding of antigen and the preassembled Cas12a-crRNA complex to the antigen-specific aptamer, resulting in a change in the collateral cleavage activity of Cas12a. To further generate an electrochemical signal, a DNA architecture was fabricated by in situ rolling circle amplification on a gold electrode, which serves as a novel substrate for Cas12a. Upon Cas12a-based collateral DNA cleavage, the DNA architecture was degraded, leading to a significant decrease in impedance that can be measured spectroscopically. Using SARS-CoV-2 nucleocapsid antigen as the model, the proposed CRISPR-Cas12a-based electrochemical sensor (CRISPR-E) showed excellent analytical performance for the quantitative detection of nucleocapsid antigen. Since in vitro selection can obtain aptamers selective for many SARS-CoV-2 antigens, the proposed strategy can expand this powerful CRISPR-E system significantly for quantitative monitoring of a wide range of COVID-19 biomarkers.

Target-Responsive Smart Nanomaterials via a Au-S Binding Encapsulation Strategy for Electrochemical/Colorimetric Dual-Mode Paper-Based Analytical Devices

Target-responsive nanomaterials attract growing interest in the application of drug delivery, bioimaging, and sensing due to the responsive releasing of guest molecules by the smart molecule gate. However, it remains a challenge to develop smart nanomaterials with simple assembly and low nonspecific leakage starting from encapsulation strategies, especially in the sensing field. Herein, Au nanoclusters (Au NCs) were first grown on porous carbon derived from ZIF-8 (PCZIF) to be employed as nanocarriers. By employing the Au NCs as linkers and aptamer (Apta) double-strand hybrids (target Apta and SH-complementary DNA) as capping units, we reported the novel target-responsive nanomaterials of Apta/Au NCs-PCZIF/hemin through Au-S binding encapsulation for sensing assays. The Au-S binding encapsulation strategy simplified the packaging procedure and reduced non-target responsive leakage. As a proof, ochratoxin A (OTA) as a model target participates in the double-strand hybrid competitive displacement reaction and triggered Apta conformation switches from a coil to a G-quadruplex structure accompanied by the dissociation of the gatekeeper. Simultaneously, the released hemin can initiate a self-assembly to form G-quadruplex/hemin DNAzyme. Interestingly, owing to DNAzyme providing electron transfer mediators and peroxidase-like activity, we proposed an electrochemical/colorimetric dual-mode paper-based analytical device (PAD) that provided self-verification to enhance reliability and accuracy, benefiting from independent signal conversion and transmission mechanism. As a consequence, the proposed dual-mode PAD could achieve sensitive electrochemical detection and visual prediction of OTA in the range of 1 pg/mL to 500 ng/mL and 50 pg/mL to 500 ng/mL, respectively. The electrochemical detection limit for OTA was as low as 0.347 pg/mL (S/N = 3). We believe that this work provides point-of-care testing (POCT) tools for a broad spectrum of applications.

Accelerated Electron Transfer in Nanostructured Electrodes Improves the Sensitivity of Electrochemical Biosensors

Electrochemical biosensors hold the exciting potential to integrate molecular detection with signal processing and wireless communication in a miniaturized, low-cost system. However, as electrochemical biosensors are miniaturized to the micrometer scale, their signal-to-noise ratio degrades and reduces their utility for molecular diagnostics. Studies have reported that nanostructured electrodes can improve electrochemical biosensor signals, but since the underlying mechanism remains poorly understood, it remains difficult to fully exploit this phenomenon to improve biosensor performance. In this work, electrochemical aptamer biosensors on nanoporous electrode are optimized to achieve improved sensitivity by tuning pore size, probe density, and electrochemical measurement parameters. Further, a novel mechanism in which electron transfer is physically accelerated within nanostructured electrodes due to reduced charge screening, resulting in enhanced sensitivity is proposed and experimentally validated. In concert with the increased surface areas achieved with this platform, this newly identified effect can yield an up to 24-fold increase in signal level and nearly fourfold lower limit of detection relative to planar electrodes with the same footprint. Importantly, this strategy can be generalized to virtually any electrochemical aptamer sensor, enabling sensitive detection in applications where miniaturization is a necessity, and should likewise prove broadly applicable for improving electrochemical biosensor performance in general.

Redox Host-Guest Nanosensors Installed with DNA Gatekeepers for Immobilization-Free and Ratiometric Electrochemical Detection of miRNA

Electrochemical nanosensors by integrating functional nucleic acids and nanomaterials hold a great promise in the fast detection of biomarkers, yet the current systems possess limitations on the accessibility of target-probe and probe-electrode interactions and the repeatability of detection. Herein, a host-guest assembly strategy is developed to build redox nanosensors for an immobilization-free and ratiometric electrochemical detection system. Specifically, electroactive molecule (E_m ) guests are loaded in porous hosts of polydopamine nanoparticles (MPDA) to act as dual-signal redox reporters. Hybrid DNA probes of G-quadruplex and a single-stranded anchor DNA are installed as gatekeepers for sealing the mesopores. Thereby, miRNA triggered E_m release by strand displacement reactions and the homogeneous transportation of the hosts/guests to the electrode facilitate the generation of reference signal/response signal at different potentials. Concomitantly applied NIR irradiation boosts the electron transfer from MPDA to the electrode and results in a tenfold increase in the reference signal. Finally, the sensing system through the differential pulse voltammetry method achieves a highly repeatable detection (relative standard deviation 3.8%) of miRNA with a lower detection limit (362 × 10^-15 m). This attractive system paves the way for rational designs of advanced electrochemical biosensors and smart diagnosis.

Design of a Waste Paper-Derived Chemically 'Reactive' and Durable Functional Material with Tailorable Mechanical Property Following an Ambient and Sustainable Chemical Approach

Controlled tailoring of mechanical property and wettability is important for designing various functional materials. The integration of these characteristics with waste materials is immensely challenging to achieve, however, it can provide sustainable solutions to combat relevant environmental pollutions and other relevant challenges. Here, the strategic conversion of discarded and valueless waste paper into functional products has been introduced following a catalyst-free chemical approach to tailor both the mechanical property and water wettability at ambient conditions for sustainable waste management and controlling the relevant environmental pollution. In the current design, the controlled and appropriate silanization of waste paper allowed to modulate both the a) porosity and b) compressive modulus of the paper-derived sponges. Further, the association of 1,4-conjugate addition reaction between amine and acrylate groups allowed to obtain an unconventional waste paper-derived chemically 'reactive' sponge. The appropriate covalent modification of the residual reactive acrylate groups with selected alkylamines at ambient conditions provided a facile basis to tailor the water wettability from moderate hydrophobicity, adhesive superhydrophobicity to non-adhesive superhydrophobicity. The embedded superhydrophobicity in the waste paper-derived sponge was capable of sustaining large physical deformations, severe physical abrasions, prolonged exposure to harsh aqueous conditions, etc. Further, the waste paper-derived, extremely water-repellent sponges and membranes were successfully extended for proof-of-concept demonstration of a practically relevant outdoor application, where the repetitive remediation of oil spillages has been demonstrated following both selective absorption (25 times) of oils and gravity-driven filtration-based (50 times) separation of oils from oil/water mixtures at different harsh aqueous scenarios.

Aptamer-Integrated Multianalyte-Detecting Paper Electrochemical Device

On-site detection of multiple small-molecule analytes in complex sample matrixes would be highly valuable for diverse biosensing applications. Paper electrochemical devices (PEDs) offer an especially appealing sensing platform for such applications due to their low cost, portability, and ease of use. Using oligonucleotide-based aptamers as biorecognition elements, we here for the first time have developed a simple, inexpensive procedure for the fabrication of aptamer-modified multiplex PEDs (mPEDs), which can robustly and specifically detect multiple small molecules in complex samples. These devices are prepared via an ambient vacuum filtration technique using carbon and metal nanomaterials that yields precisely patterned sensing architecture featuring a silver pseudo-reference electrode, a gold counter electrode, and three gold working electrodes. The devices are user-friendly, and the fabrication procedure is highly reproducible. Each working electrode can be readily modified with different aptamers for sensitive and accurate detection of multiple small-molecule analytes in a single sample within seconds. We further demonstrate that the addition of a PDMS chamber allows us to achieve detection in microliter volumes of biological samples. We believe this approach should be highly generalizable, and given the rapid development of small-molecule aptamers, we envision that facile on-site multi-analyte detection of diverse targets in a drop of sample should be readily achievable in the near future.

Aptamer-Functionalized Hybrid Nanostructures for Sensing, Drug Delivery, Catalysis and Mechanical Applications

Sequence-specific nucleic acids exhibiting selective recognition properties towards low-molecular-weight substrates and macromolecules (aptamers) find growing interest as functional biopolymers for analysis, medical applications such as imaging, drug delivery and even therapeutic agents, nanotechnology, material science and more. The present perspective article introduces a glossary of examples for diverse applications of aptamers mainly originated from our laboratory. These include the introduction of aptamer-functionalized nanomaterials such as graphene oxide, Ag nanoclusters and semiconductor quantum dots as functional hybrid nanomaterials for optical sensing of target analytes. The use of aptamer-functionalized DNA tetrahedra nanostructures for multiplex analysis and aptamer-loaded metal-organic framework nanoparticles acting as sense-and-treat are introduced. Aptamer-functionalized nano and microcarriers are presented as stimuli-responsive hybrid drug carriers for controlled and targeted drug release, including aptamer-functionalized SiO2 nanoparticles, carbon dots, metal-organic frameworks and microcapsules. A further application of aptamers involves the conjugation of aptamers to catalytic units as a means to mimic enzyme functions "nucleoapzymes". In addition, the formation and dissociation of aptamer-ligand complexes are applied to develop mechanical molecular devices and to switch nanostructures such as origami scaffolds. Finally, the article discusses future challenges in applying aptamers in material science, nanotechnology and catalysis.