An Aptamer-Based Capacitive Sensing Platform for Specific Detection of Lung Carcinoma Cells in the Microfluidic Chip

A liquid crystal-decorated aptasensing gadget for rapid monitoring of A549 cells: Future portable test kit for lung cancer diagnosis

BACKGROUND

Presented here is a straightforward detection system designed to track non-small cell lung cancer (specifically A549 cells) using a combination of liquid crystals (LCs) and aptamer sequences, marking a pioneering approach in this field. A change in the alignment of LCs from perpendicular to random status by the aptamer-cell complex altered the murky polarized background of the aptasensor to multicolored.

RESULTS

The LC-designed aptasensor could determine A549 cancerous cells in the range of 2.0E+01-7.0E+07 cell mL-1 with a limit of detection (LOD) as low as 10 cell mL-1. Through precise quantification of A549 cells in human serum samples diluted 20 times, with recovery rates ranging from 97.59 % to 101.31 %, the suggested aptasensor proves to be a dependable method for cancer screening. Furthermore, the LC aptasensor was identified as a fast sensing array due to a 10-min incubation period for the aptamer-cell complexation.

SIGNIFICANCE

The LC aptasensor is label-free, operator-independent, low-cost, sensitive, and user-friendly, making it potent as a miniaturized portable sensing chip for efficient healthcare monitoring.

Based on mutated aptamer-smartphone colorimetric detection of metronidazole in milk

Excessive residue of metronidazole (MNZ) in food is harmful to the human body. There is an urgent demand to develop a portable tool for MNZ detection on-site. In this study, fifteen aptamers were prepared through targeted base mutation. Apt1-3 with the highest enrichment was chosen for further study. Its affinity was characterized by molecular docking simulation, AuNPs colorimetric assay, graphene oxide (GO) fluorescence assay, and exonuclease assay. Kd was determined by GO fluorescence assay (Kd: 92.60 ± 25.59 nM). Its specificity was also characterized by an exonuclease assay. A novel aptasensor was constructed by using the newly identified aptamer combined with the smartphone dark box. The principle of color change is caused by the aggregation state of AuNPs. Smartphones act as reading instruments. The detection can be completed in just a few seconds without the aid of instruments, achieving a detection limit of 0.15 nmol/mL and a range of 6.7-44.4 nmol/mL (R 2 = 0.9810). Therefore, the constructed smartphone colorimetric sensor based on mutant aptamers has important applications in food detection.

Parylene Double-Layer Coated Screen-Printed Carbon Electrode for Label-Free and Reagentless Capacitive Aptasensing of Gliadin

Celiac patients are required to strictly adhere to a gluten-free diet because even trace amounts of gluten can damage their small intestine and leading to serious complications. Despite increased awareness, gluten can still be present in products due to cross-contamination or hidden ingredients, making regular monitoring essential. With the goal of guaranteeing food safety for consuming labeled gluten-free products, a capacitive aptasensor was constructed to target gliadin, the main allergic gluten protein for celiac disease. The success of capacitive aptasensing was primarily realized by coating a Parylene double-layer (1000 nm Parylene C at the bottom with 400 nm Parylene AM on top) on the electrode surface to ensure both high insulation quality and abundant reactive amino functionalities. Under the optimal concentration of aptamer (5 μM) used for immobilization, a strong linear relationship exists between the amount of gliadin (0.01-1.0 mg/mL) and the corresponding ΔC response (total capacitance decrease during a 20 min monitoring period after sample introduction), with an R2 of 0.9843. The detection limit is 0.007 mg/mL (S/N > 5), equivalent to 0.014 mg/mL (14 ppm) of gluten content. Spike recovery tests identified this system is free from interferences in corn and cassava flour matrices. The analytical results of 24 commercial wheat flour samples correlated well with a gliadin ELISA assay (R2 = 0.9754). The proposed label-free and reagentless capacitive aptasensor offers advantages of simplicity, cost-effectiveness, ease of production, and speediness, making it a promising tool for verifying products labeled as gluten-free (gluten content <20 ppm).

Efficient detection of single circulating tumor cell in blood using Raman mapping based on Aptamer-SERS bio-probe coupled with micropore membrane filtration

Rapid and accurate detection of rare circulating tumor cells (CTCs) in human blood still remains a challenge. We present a surface enhanced Raman spectroscopy (SERS) method based on aptamer-SERS bio-probe recognition coupled with micropore membrane filtration capture for the detection of CTCs at single cell level. The parylene micropore membrane with optimized micropore size installed on a filtration holder could capture bio-probe labeled CTCs by gravity in less than 10 s, and only with very less white blood cells (WBCs) residual. In order to facilitate the synthesis of the aptamer-SERS bio-probe, ethyl acetate dehydration method was established. The bio-probe can be rapidly synthesized within 2 h by binding SH-aptamer to 4- mercaptobenzoic acid (4-MBA) modified AuNPs with the help of ethyl acetate. The SERS bio-probe with selected specific aptamer could distinguish single human non-small cell lung cancer A549 cells from residual WBCs on membrane efficiently and reliably based on their Raman signal intensity difference at 1075 cm-1. Through the filter membrane coupled with aptamer-SERS bio-probe system, even 20 A549 cells in blood solution simulating CTCs sample can be detected, which the recovery rate and recognition rate are more than 90%. This method is rapid, reliable and cost-effective, which indicates a good prospect in clinical application for CTCs detection.

The effect of magnetic bead size on the isolation efficiency of lung cancer cells in a serpentine microchannel with added cavities

An investigation was conducted to examine the effect of magnetic bead (MB) size on the effectiveness of isolating lung cancer cells using the immunomagnetic separation (IMS) method in a serpentine microchannel with added cavities (SMAC) structure. Carboxylated magnetic beads were specifically conjugated to target cells through a modification procedure using aptamer materials. Cells immobilized with different sizes (in micrometers) of MBs were captured and isolated in the proposed device for comparison and analysis. The study yields significance regarding the clarification of device working principles by using a computational model. Furthermore, an accurate evaluation of the MB size impact on capture efficiency was achieved, including the issue of MB-cell accumulation at the inlet-channel interface, despite it being overlooked in many previous studies. As a result, our findings demonstrated an increasing trend in binding efficiency as the MB size decreased, evidenced by coverages of 50.5%, 60.1%, and 73.4% for sizes of 1.36 μm, 3.00 μm, and 4.50 μm, respectively. Additionally, the overall capture efficiency (without considering the inlet accumulation) was also higher for smaller MBs. However, when accounting for the actual number of cells entering the channel (i.e., the effective capture), larger MBs showed higher capture efficiency. The highest effective capture achieved was 88.4% for the size of 4.50 μm. This research provides an extensive insight into the impact of MB size on the performance of IMS-based devices and holds promise for the efficient separation of circulating cancer cells (CTCs) in practical applications.

Capacitive biosensors for label-free and ultrasensitive detection of biomarkers

Capacitive biosensors are label-free capacitors that can detect biomarkers with the outstanding advantages of simplicity, low cost, and ultrahigh sensitivity. A typical capacitive biosensor consists of a bioreceptor and a transducer, where the bioreceptor captures the biomarker to form a bioreceptor/biomarker conjugate and the transducer generates a detectable signal. In general, antibodies, aptamers, or proteins are exploited as the bioreceptor, while various electrodes including carbon electrodes (CEs), gold electrodes (AuEs), or interdigitated electrodes (IDEs) may serve as the transducer. Because the formation of bioreceptor/biomarker conjugates often leads to a change in capacitance, the capacitive signal is then employed for biomarker detection. This review summarizes recent advances in capacitive biosensors for the detection of biomarkers over the last five years. With a focus on the three common types of bioreceptors, i.e., antibodies, aptamers, and proteins, capacitive biosensors using CEs, AuEs, and IDEs as the transducers are discussed in detail. The immobilization of bioreceptors and signal amplification strategies are described to provide a robust overview of capacitive biosensors for biomarker detection. In addition, analytical methods and future prospects are given to support the application of capacitive biosensors.

Recent advances in nanobiosensors for sustainable healthcare applications: A systematic literature review

The need for novel healthcare treatments and drugs has increased due to the expanding human population, detection of newer diseases, and looming pandemics. The development of nanotechnology offers a platform for cutting-edge in vivo non-invasive monitoring and point-of-care-testing (POCT) for rehabilitative disease detection and management. The advancement and uses of nanobiosensors are currently becoming more common in a variety of scientific fields, such as environmental monitoring, food safety, biomedical, clinical, and sustainable healthcare sciences, since the advent of nanotechnology. The identification and detection of biological patterns connected to any type of disease (communicable or not) have been made possible in recent years by several sensing techniques utilizing nanotechnology concerning biosensors and nanobiosensors. In this work, 2218 articles are drawn and screened from six digital databases out of which 17 were shortlisted for this review by using the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) technique. As a result, this study uses a systematic methodology to review some recently developed extremely sensitive nanobiosensors, along with their biomedical, point-of-care diagnostics (POCD), or healthcare applications and their capabilities, particularly for the prediction of some fatal diseases based on a few of the most recent publications. The potential of nanobiosensors for medicinal, therapeutic, or other sustainable healthcare applications, notably for ailments diagnostics, is also recognized as a way forward in the manifestation of future trends.

Metallic Nanowires Self-Assembled in Quasi-Circular Nanomolds Templated by DNA Origami

The self-assembly of conducting nanostructures is currently being investigated intensively in order to evaluate the feasibility of creating novel nanoelectronic devices and circuits using such pathways. In particular, methods based on so-called DNA Origami nanostructures have shown great potential in the formation of metallic nanowires. The main challenge of this method is the reproducible generation of very well-connected metallic nanostructures, which may be used as interconnects in future devices. Here, we use a novel design of nanowires with a quasi-circular cross-section as opposed to rectangular or uncontrolled cross-sections in earlier studies. We find indications that the reliability of the fabrication scheme is enhanced and the overall resistance of the wires is comparable to metallic nanostructures generated by electrochemistry or top-down methods. In addition, we observe that some of the nanowires are annealed when passing a current through them, which leads to a clear enhancement for the conductance. We envision that these nanowires provide further steps towards the successful generation of nanoelectronics using self-assembly.

Aptamer-functionalized capacitive biosensors

The growing use of aptamers as target recognition elements in label-free biosensing necessitates corresponding transducers that can be used in relevant environments. While popular in many fields, capacitive sensors have seen relatively little, but growing use in conjunction with aptamers for sensing diverse targets. Few reports have shown physiologically relevant sensitivity in laboratory conditions and a cohesive picture on how target capture modifies the measured capacitance has been lacking. In this review, we assess the current state of the field in three areas: small molecule, protein, and cell sensing. We critically analyze the proposed hypotheses on how aptamer-target capture modifies the capacitance, as many mechanistic postulations appear to conflict between published works. As the field matures, we encourage future works to investigate individual aptamer-target interactions and to interrogate the physical mechanisms leading to measured changes in capacitance. To this point, we provide recommendations on best practices for developing aptasensors with a particular focus on considerations for biosensing in clinical settings.

Microfluidic-Chip-Integrated Biosensors for Lung Disease Models

Lung diseases (e.g., infection, asthma, cancer, and pulmonary fibrosis) represent serious threats to human health all over the world. Conventional two-dimensional (2D) cell models and animal models cannot mimic the human-specific properties of the lungs. In the past decade, human organ-on-a-chip (OOC) platforms-including lung-on-a-chip (LOC)-have emerged rapidly, with the ability to reproduce the in vivo features of organs or tissues based on their three-dimensional (3D) structures. Furthermore, the integration of biosensors in the chip allows researchers to monitor various parameters related to disease development and drug efficacy. In this review, we illustrate the biosensor-based LOC modeling, further discussing the future challenges as well as perspectives in integrating biosensors in OOC platforms.

Immunomagnetic separation in a novel cavity-added serpentine microchannel structure for the selective isolation of lung adenocarcinoma cells

The manipulation and separation of circulating tumor cells (CTCs) in continuous fluidic flows play an essential role in various biomedical applications, particularly the early diagnosis and treatment of diseases. Recent advances in magnetic bead development have provided promising solutions to the challenges encountered in CTC manipulation and isolation. In this study, we proposed a biomicrofluidic platform for specifically isolating human lung carcinoma A549 cells in microfluidic channels. The principle of separation was based on the effect of the magnetic field on aptamer-conjugated magnetic beads, also known as immunomagnetic beads, in a serpentine microchannel with added cavities (SMAC). The magnetic cell separation performance of the proposed structure was modeled and simulated by using COMSOL Multiphysics. The experimental procedures for aptamer molecular conjugation on 1.36 µm-diameter magnetic beads and magnetic bead immobilization on A549 cells were also reported. The lung carcinoma cell-bead complexes were then experimentally separated by an external magnetic field. Separation performance was also confirmed by optical microscopic observations and fluorescence analysis, which showed the high selectivity and efficiency of the proposed system in the isolation and capture of A549 cells in our proposed SMAC. At the flow rate of 5 µL/s, the capture rate of human lung carcinoma cells exceeded 70% in less than 15 min, whereas that of the nontarget cells was approximately 4%. The proposed platform demonstrated its potential for high selectivity, portability, and facile operation, which are suitable considerations for developing point-of-care applications for various biological and clinical purposes.

Electrochemical sensing technology for liquid biopsy of circulating tumor cells-a review

In recent years, a lot of new detection techniques for circulating tumor cells (CTCs) have been developed. Among them, electrochemical sensing technology has gradually developed because of its advantages of good selectivity, high sensitivity, low cost and rapid detection. Especially in the latest decade, the field of electrochemical biosensing has witnessed great progress, thanks to the merging of biosensing research area with nanotechnology, immunotechnology, nucleic acid technology, and microfluidic technology. In this review, the recent progress for the detection of CTCs according to the principle of detection was summarized and how they can contribute to the enhanced performance of such biosensors was explained. The latest electrode construction strategies such as rolling circle amplification reaction, DNA walker and microfluidic technology and their advantages were also introduced emphatically. Moreover, the main reasonswhy the existing biosensors have not been widely used clinically and the next research points were clearly put forward.

Aptamer-Based Detection of Circulating Targets for Precision Medicine

The past decade has witnessed ongoing progress in precision medicine to improve human health. As an emerging diagnostic technique, liquid biopsy can provide real-time, comprehensive, dynamic physiological and pathological information in a noninvasive manner, opening a new window for precision medicine. Liquid biopsy depends on the sensitive and reliable detection of circulating targets (e.g., cells, extracellular vesicles, proteins, microRNAs) from body fluids, the performance of which is largely governed by recognition ligands. Aptamers are single-stranded functional oligonucleotides, capable of folding into unique tertiary structures to bind to their targets with superior specificity and affinity. Their mature evolution procedure, facile modification, and affinity regulation, as well as versatile structural design and engineering, make aptamers ideal recognition ligands for liquid biopsy. In this review, we present a broad overview of aptamer-based liquid biopsy techniques for precision medicine. We begin with recent advances in aptamer selection, followed by a summary of state-of-the-art strategies for multivalent aptamer assembly and aptamer interface modification. We will further describe aptamer-based micro-/nanoisolation platforms, aptamer-enabled release methods, and aptamer-assisted signal amplification and detection strategies. Finally, we present our perspectives regarding the opportunities and challenges of aptamer-based liquid biopsy for precision medicine.

Effective Isolation for Lung Carcinoma Cells Based on Immunomagnetic Separation in a Microfluidic Channel

In this paper, we developed an isolation system for A549 human lung carcinoma cells as an effective factor for the early diagnosis of lung cancer. A microfluidic immunomagnetic method was used, in which the combination of immunomagnetic separation and a microfluidic system allowed for increased isolation efficiency with uncomplicated manipulation. In the microfluidic immunomagnetic strategy, A549 cells were combined with aptamer-conjugated carboxylated magnetic beads and then collected in a specified region by applying a magnetic field. The results were recorded using a fluorescence microscope, and the captured targets were then quantified. The isolation efficiency of A549 cells is up to 77.8%. This paper developed a simple working procedure, which is less time consuming, high-throughput, and trustworthy for the isolation of A549 cells. This procedure can be a useful reference method for the development of an effective diagnosis and treatment method for lung cancer in the future.

Biosensors-on-Chip: An Up-to-Date Review

Generally, biosensors are designed to translate physical, chemical, or biological events into measurable signals, thus offering qualitative and/or quantitative information regarding the target analytes. While the biosensor field has received considerable scientific interest, integrating this technology with microfluidics could further bring significant improvements in terms of sensitivity and specificity, resolution, automation, throughput, reproducibility, reliability, and accuracy. In this manner, biosensors-on-chip (BoC) could represent the bridging gap between diagnostics in central laboratories and diagnostics at the patient bedside, bringing substantial advancements in point-of-care (PoC) diagnostic applications. In this context, the aim of this manuscript is to provide an up-to-date overview of BoC system development and their most recent application towards the diagnosis of cancer, infectious diseases, and neurodegenerative disorders.

Aptamer-based electrochemical biosensing strategy toward human non-small cell lung cancer using polyacrylonitrile/polypyrrole nanofibers

In the present study, a sensitive electrochemical aptamer-based biosensing strategy for human non-small cell lung cancer (NSCLC) detection was proposed using nanofiber-modified disposable pencil graphite electrodes (PGEs). The composite nanofiber was comprised of polyacrylonitrile (PAN) and polypyrrole (PPy) polymers, and fabrication of the nanofibers was accomplished using electrospinning process onto PGEs. Development of the nanofibers was confirmed using scanning electron microscopy (SEM). The high-affinity 5'-aminohexyl-linked aptamer was immobilized onto a PAN/PPy composite nanofiber-modified sensor surface via covalent bonding strategy. After incubation with NSCLC living cells (A549 cell line) at 37.5 °C, the recognition between aptamer and target cells was monitored by electrochemical impedance spectroscopy (EIS). The selectivity of the aptasensor was evaluated using nonspecific human cervical cancer cells (HeLa) and a nonspecific aptamer sequence. The proposed electrochemical aptasensor showed high sensitivity toward A549 cells with a detection limit of 1.2 × 10³ cells/mL. The results indicate that our label-free electrochemical aptasensor has great potential in the design of aptasensors for the diagnostics of other types of cancer cells with broad detection capability in clinical analysis. Graphical abstract.

An integrated microfluidic platform for selective and real-time detection of thrombin biomarkers using a graphene FET

Lab-on-a-chip technology offers an ideal platform for low-cost, reliable, and easy-to-use diagnostics of key biomarkers needed for early screening of diseases and other health concerns. In this work, a graphene field-effect transistor (GFET) functionalized with target-binding aptamers is used as a biosensor for the detection of thrombin protein biomarker. Furthermore, this GFET is integrated with a microfluidic device for enhanced sensing performances in terms of detection limit, sensitivity, and continuous monitoring. Under this platform, a picomolar limit of detection was achieved for measuring thrombin; in our experiment measured as low as 2.6 pM. FTIR, Raman and UV-Vis spectroscopy measurements were performed to confirm the device functionalization steps. Based on the concentration-dependent calibration curve, a dissociation constant of KD = 375.8 pM was obtained. Continuous real-time measurements were also conducted under a constant gate voltage (VGS) to observe the transient response of the sensor when analyte was introduced to the device. The target selectivity of the sensor platform was evaluated and confirmed by challenging the GFET biosensor with various concentrations of lysozyme protein. The results suggest that this device technology has the potential to be used as a general diagnostic platform for measuring clinically relevant biomarkers for point-of-care applications.

Combining impedance biosensor with immunomagnetic separation for rapid screening of Salmonella in poultry supply chains

Salmonella screening is a key to ensure food safety in poultry supply chains. Currently available Salmonella detection methods including culture, polymerase chain reaction and enzyme-linked immuno-sorbent assay could not achieve rapid, sensitive, and in-field detection. In this study, different strategies for separation and detection of Salmonella were proposed, compared, and improved based on our previous studies on immunomagnetic separation and impedance biosensor. First, the coaxial capillary for immunomagnetic separation of target bacteria was improved with less contamination, and 3 strategies based on the improved capillary and immunomagnetic nanoparticles were compared to separate the target bacteria from sample and form the magnetic bacteria. The experimental results showed that the strategy of capture in tube and separation in capillary was the most suitable with separation efficiency of approximately 88%. Then, the immune gold nanoparticles coated with urease were used to label the magnetic bacteria, resulting in the formation of enzymatic bacteria, which were injected into the capillary. After the urea was catalyzed by the urease on the enzymatic bacteria in the capillary, different electrodes were compared to measure the impedance of the catalysate and the screen-printed electrode with higher sensitivity and better stability was the most suitable. This impedance biosensor-based bacterial detection strategy was able to detect Salmonella as low as 102 CFU/mL in 2 h without complex operations. Compared to the gold standard culture method for practical screening of Salmonella in poultry supply chains, this proposed strategy had an accuracy of approximately 90% for 75 real poultry samples.

Lab-on-a-Chip Systems for Aptamer-Based Biosensing

Aptamers are oligonucleotides or peptides that are selected from a pool of random sequences that exhibit high affinity toward a specific biomolecular species of interest. Therefore, they are ideal for use as recognition elements and ligands for binding to the target. In recent years, aptamers have gained a great deal of attention in the field of biosensing as the next-generation target receptors that could potentially replace the functions of antibodies. Consequently, it is increasingly becoming popular to integrate aptamers into a variety of sensing platforms to enhance specificity and selectivity in analyte detection. Simultaneously, as the fields of lab-on-a-chip (LOC) technology, point-of-care (POC) diagnostics, and personal medicine become topics of great interest, integration of such aptamer-based sensors with LOC devices are showing promising results as evidenced by the recent growth of literature in this area. The focus of this review article is to highlight the recent progress in aptamer-based biosensor development with emphasis on the integration between aptamers and the various forms of LOC devices including microfluidic chips and paper-based microfluidics. As aptamers are extremely versatile in terms of their utilization in different detection principles, a broad range of techniques are covered including electrochemical, optical, colorimetric, and gravimetric sensing as well as surface acoustics waves and transistor-based detection.

Selective Detection of Human Lung Adenocarcinoma Cells Based on the Aptamer-Conjugated Self-Assembled Monolayer of Gold Nanoparticles

This study established a microfluidic chip for the capture of A549 human lung circulating tumor cells via the aptamer-conjugated self-assembled monolayer (SAM) of gold nanoparticles (AuNPs) in the channel. AuNPs are among the most attractive nanomaterials for the signal enhancement of biosensors owing to their unique chemical, physical, and mechanical properties. The microchip was fabricated using soft photolithography and casting and molding techniques. A self-assembly method was designed to attach AuNPs, cell-specific aptamers, and target cells onto the desired area (i.e., SAM area). In this study, the gold microelectrode configuration was characterized by fluorescence microscopy and impedance measurements to confirm the important modification steps. Subsequently, several investigations with the proposed assay were conducted with different cell samples to determine the specific binding ability of the device for A549 adenocarcinoma cancer cells. This work has ensured a simple, convenient, selective, and sensitive approach for the development of biosensors for lung cancer detection during the early stages.