A paper-based electrochemiluminescence electrode as an aptamer-based cytosensor using PtNi@carbon dots as nanolabels for detection of cancer cells and for in-situ screening of anticancer drugs

Paper-Based Aptasensors: Working Principles, Detection Modes, and Applications

Aptamers are short oligonucleotides designed to possess high binding affinity towards specific target compounds (ions, molecules, or cells). Due to their function and unique advantages, aptamers are considered viable alternatives to antibodies as biorecognition elements in bioassays and biosensors. On the other hand, paper-based devices (PADs) have emerged as a promising and powerful technology for the fabrication of low-cost analytical tools, mainly intended for on-site and point-of-care applications. The present work aims to provide a comprehensive overview of paper-based aptasensors. The review describes the fabrication methods and working principles of paper-based devices, the properties of aptamers as bioreceptors, the different modes of detection used in conjunction with aptasensing PADs, and representative applications for the detection of ions, small molecules, proteins, and cells. The future challenges and prospects of these devices are also discussed.

Role of Paper-Based Sensors in Fight against Cancer for the Developing World

Cancer is one of the major killers across the globe. According to the WHO, more than 10 million people succumbed to cancer in the year 2020 alone. The early detection of cancer is key to reducing the mortality rate. In low- and medium-income countries, the screening facilities are limited due to a scarcity of resources and equipment. Paper-based microfluidics provide a platform for a low-cost, biodegradable micro-total analysis system (µTAS) that can be used for the detection of critical biomarkers for cancer screening. This work aims to review and provide a perspective on various available paper-based methods for cancer screening. The work includes an overview of paper-based sensors, the analytes that can be detected and the detection, and readout methods used.

Optical cytosensors for the detection of circulating tumour cells

Blood analysis is an established approach to monitor various diseases, ranging from heart defects and diabetes to cancer. Among various tumor markers in the blood, circulating tumor cells (CTCs) have received increasing attention due to the fact that they originate directly from the tumors. Capturing and detecting CTCs represents a promising approach in cancer diagnostics and clinical management of cancers. CTCs in blood progress to self-seeding a tumour or initiating a new lesion mass. Cytosensors are biosensors intended to identify CTCs in a blood sample of cancer patients and provide information about the cancer status. Herein, we firstly discuss different detection methods of state-of-the-art optical cytosensors, including colorimetry, fluorescence, surface plasmon resonance, photoelectrochemistry and electrochemiluminescence. Then we review the significant advances made in implementing biorecognition elements and nanomaterials for the detection of cancer cells. Despite great progress in optical cytosensors, and their integration with smartphones, they have still only been explored to prototype stages. Much more effort is needed to fulfil their potential in modern cancer diagnostics and in monitoring the state of disease for cancer patients.

Recent Advances and Applications in Paper-Based Devices for Point-of-Care Testing

Point-of-care testing (POCT), as a portable and user-friendly technology, can obtain accurate test results immediately at the sampling point. Nowadays, microfluidic paper-based analysis devices (μPads) have attracted the eye of the public and accelerated the development of POCT. A variety of detection methods are combined with μPads to realize precise, rapid and sensitive POCT. This article mainly introduced the development of electrochemistry and optical detection methods on μPads for POCT and their applications on disease analysis, environmental monitoring and food control in the past 5 years. Finally, the challenges and future development prospects of μPads for POCT were discussed.

Nano-functionalized paper-based IoT enabled devices for point-of-care testing: a review

Over the last few years, the microfluidics phenomenon coupled with the Internet of Things (IoT) using innovative nano-functional materials has been recognized as a sustainable and economical tool for point-of-care testing (POCT) of various pathogens influencing human health. The sensors based on these phenomena aim to be designed for cost-effectiveness, make it handy, environment-friendly, and get an accurate, easy, and rapid response. Considering the burgeoning importance of analytical devices in the healthcare domain, this review paper is based on the gist of sensing aspects of the microfabricated paper-based analytical devices (μPADs). The article discusses the various used design methodologies and fabrication approaches and elucidates the recently reported surface modification strategies, detection mechanisms viz., colorimetric, electrochemical, fluorescence, electrochemiluminescence, etc. In a nutshell, this article summarizes the state-of-the-art research work carried out over the nano functionalized paper-based analytical devices and associated challenges/solutions in the point of care testing domain.

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.

A highly sensitive electrochemiluminescence cytosensor for detection of SKBR-3 cells as metastatic breast cancer cell line: A constructive phase in early and precise diagnosis

Ultrasensitive monitoring of cancer cells, especially metastatic ones, has a great interest in human medicine. Despite the early diagnosis of diseases, there is an essential need for any prediction in the severity of side effects for therapeutic outcomes like metastasis. Therefore, the inhibition of cancer cells metastasis to other organs is of utmost importance for cancer suffering patients. In this regard, we developed an electrochemiluminescence (ECL)-based cytosensor for the quantification of metastatic breast cancer cells, namely SKBR-3. Silica-based mesoporous materials have a great potential for application in ECL biosensors due to their high loading capacity and mechanical strength. Herein, a silica-based electrode was prepared via in situ electrosyntheses of mesoporous silica as an environmentally friendly approach. In this protocol, luminol (as luminophore) was combined with chitosan (as attachment biomolecule) to produce a stable lumino-composite film on the electrode surface. At the optimum experimental conditions, the lower limit of quantitation (LLOQ) and linear dynamic range (LDR) were obtained as 20 cells/mL and 20 to 2000 cells/mL, individually. The specificity was desirably examined in the presence of other breast cancer cell lines such as MCF-7 and MDA-MB-231, as a model of early-stage and invasive phases of breast cancer cells. The repeatability was successfully examined for five repetitive measurements and the acceptable relative standard deviation (RSD) was calculated as about 1.6% for 500 cells/mL. As a proof of concept, the presented cytosensor has a high ability to use in clinical laboratories for the detection and separation of metastatic cells via the combination with microfluidic systems.

Industry Development of Derivative Functionalized Gold Nanomaterials and Their Application in Chemiluminescence Bioanalysis: Based on the Industrial Practice of China's Central Yunnan Urban Agglomeration

Electrochemiluminescence biosensor is an analytical method combining electrochemiluminescence technology with biosensor. Using nanomaterials as electrochemical luminescence sensor platform can not only immobilize a large number of biomolecules but also improve the performance of the sensor to realize the supersensitive detection of biomacromolecules. Although these methods have high sensitivity for bioanalysis, there are still some shortcomings which limit the practical application. Therefore, this paper discusses the development of functional gold nanomaterials industry and its application in chemiluminescence bioanalysis. In this paper, two methods of synthesizing luminescent functional gold nanomaterials at room temperature were studied by using chemiluminescent reagents as reducing agent and protective agent. Based on luminescent functionalized gold nanoparticles, immunoassay and DNA bioanalysis probes were constructed, and their applications in chemiluminescence and electrochemiluminescence bioanalysis were discussed. Finally, the simulation results show that the relative deviation between the experimental results and the existing clinical methods is less than 17%. The sensor has good stability and selectivity and can be used for the determination of CEA in human serum. The gold nanomaterials synthesized by further research have excellent chemiluminescence activity and can be used to label biomolecules and prepare biological probes. This article aims to explore the application of chemical methods in the transformation of new industries, to achieve breakthroughs in new products in industrial innovation, and to achieve the cross-fusion of management science and engineering disciplines and chemical disciplines. The industrial development of derivative functionalized gold nanomaterials has broad application prospects in biological analysis.

Paper-based microfluidic aptasensors

For in-situ disease markers detection, point-of-care (POC) diagnosis has great advantages in speed and cost compared with traditional techniques. The rapid diagnosis, prognosis, and surveillance of diseases can significantly reduce disease-related mortality and trauma. Therefore, increasing attention has been paid to the POC diagnosis devices due to their excellent diagnosis speed and portability. Over the past ten years, paper-based microfluidic aptasensors have emerged as a class of critical POC diagnosis devices and various aptasensors have been proposed to detect various disease markers. However, most aptasensors need further improvement before they can actually enter the market and be widely used. There is thus an urgent need to sort out the key points of preparing the aptasensors and the direction that needs to be invested in. This review summarizes the representative articles in the development of paper-based microfluidic aptasensors. These works can be divided into paper-based optical aptasensors and paper-based electrochemical aptasensors according to their output signals. Significant focus is applied to these works according to the following three parts: (1) The ingenious design of device structure; (2) Application and synthesis of nanomaterial; (3) The detection principle of the proposed aptasensor. This is a detailed and comprehensive review of paper-based microfluidic aptasensors. The accomplishments and shortcomings of the current aptasensors are outlined, the development direction and the future prospective are given. It is hoped that the research in this review can provide a reference for further development of more advanced, more effective paper-based microfluidic aptasensors for POC disease markers diagnosis.

Aptamer-Modified Nanoparticles in Medical Applications

Since aptamers have been selected against a broad range of target structures of medical interest and nanoparticles are available with diverse properties, aptamer-modified nanoparticles can be used in various diagnostic and therapeutic applications. While the aptamer is responsible for specificity and affinity of the conjugate, the nanoparticles' function varies from signal generation in diagnostic approaches to drug loading in drug delivery systems. Within this chapter different medical applications of aptamer-modified nanoparticles will be summarized and underlying principles will be described.

Recognition and sensitive detection of CTCs using a controllable label-free electrochemical cytosensor

An excellent atomic layer deposition (ALD) method was adopted for the controllable systhesis of a xFe₂O₃-nPt (or nPt-xFe₂O₃)-coated graphene nanostructure (xFe₂O₃-nPt@graphene). The produced nanomaterials have been characterized by transmission electron microscopy (TEM), cyclic voltammetry (CV), and X-ray photoelectron spectroscopy (XPS). It is shown that xFe₂O₃ and nPt were effectively tailored and deposited on the graphene. A simple, rapid, and sensitive electrochemical cytosensor based on the controllable nanomaterials was successfully developed for MCF-7 cells detection by combining the high affinity and specificity of an aptamer. The prepared cytosensor displays a linear response to MCF-7 in the concentration range 18 to 1.5 × 10⁶ cell mL^-1 with the detection limit of 6 cell mL^-1 (at an S/N of 3). This cytosensor was applied to detect circulating tumor cells (CTCs) in patient blood and the results were satisfied. The experimental results indicate that the proposed controllable electrochemical cytosensor is highly-sensitive, and convenient for clinical detection of breast CTCs. Graphical abstract.

Recent developments in electrochemiluminescence nanosensors for cancer diagnosis applications

In recent years, electrochemiluminescence (ECL) nanosensing systems have undergone rapid development and made significant progress in ultrasensitive analysis and cell imaging. Because of the unique advantages of high selectivity, ultra-sensitivity, and good reproducibility, ECL nanosensors can open new paths for cancer diagnosis. With the development of ECL nanosensors, high-throughput analysis, visual detection and spatially resolved ECL imaging of single cells are being realized. The innovations of ECL nanosensors consist of electrochemical excitation, coreactant catalysis, light radiation and luminescence signal amplification, which involve several fields such as nanotechnology, catalysis, optics, and electrochemistry. The developments of ECL instruments also relate to imaging technology. Herein, we review the construction modes, sensing strategies and cancer diagnosis applications of ECL nanosenors. Firstly, the nano-components of the ECL sensing system are discussed. The construction and signal amplification methods of the nanosensing system are emphasized. Secondly, the high-efficiency cancer identification strategies are presented, including protein tumor marker detection, nucleic acid assay, cancer cell identification and exosome detection. The recent advances in representative examples of ECL nanosenors in cancer diagnosis are highlighted, including high-throughput ECL analysis, in situ assay, visual ECL detection, single-cell imaging diagnosis, and so on. Finally, the challenges are featured based on the recent development of the ECL nanosensing system in the clinical diagnosis. The ECL nanosensors provide effective and reliable analytical methods and open new paths for cancer diagnosis. It is noteworthy that the prospects of the ECL nanosensing system in clinical diagnosis are instructive to the developments of other nanosensor research.

Recent Advances in Microfluidic Paper-Based Analytical Devices toward High-Throughput Screening

Microfluidic paper-based analytical devices (µPADs) have become promising tools offering various analytical applications for chemical and biological assays at the point-of-care (POC). Compared to traditional microfluidic devices, µPADs offer notable advantages; they are cost-effective, easily fabricated, disposable, and portable. Because of our better understanding and advanced engineering of µPADs, multistep assays, high detection sensitivity, and rapid result readout have become possible, and recently developed µPADs have gained extensive interest in parallel analyses to detect biomarkers of interest. In this review, we focus on recent developments in order to achieve µPADs with high-throughput capability. We discuss existing fabrication techniques and designs, and we introduce and discuss current detection methods and their applications to multiplexed detection assays in relation to clinical diagnosis, drug analysis and screening, environmental monitoring, and food and beverage quality control. A summary with future perspectives for µPADs is also presented.

An enzyme-free fluorometric nanoprobe for chloramphenicol based on signal amplification using graphene oxide sheets

A sensitive and selective method for the determination of the antibiotic chloramphenicol (CAP) is described, which is based on double signal amplification and GO as an efficient fluorescence quencher. The nucleic acid probe is composed of three well-defined regions, viz. the signal probe I, the signal probe II, and the capture probe. The capture probe will bind to CAP specifically and the signal probes produce a significant fluorescence signal. One end of the signal probes is labeled with the fluorophore 6-carboxyfluorescein (FAM). The labeled probes can be adsorbed on graphene oxide (GO) via π-stacking interactions, upon which the green fluorescence of FAM (measured at excitation/emission wavelengths of 490/514 nm) is quenched. On addition of CAP, the aptamer/CAP complexes are formed, and this leads to the restoration of fluorescence due to the removal of the probes from GO. The double signal probes, together with GO as quencher, improve the fluorescence signal significantly and lower the detection limit. Under optimized conditions, the assay works in the 20- to 200-ppb CAP concentration range and has a 0.3-ppb detection limit. It is also successfully applied to the determination of CAP in spiked swine urine samples. The recoveries from spiked swine urine samples are between 97.73 and 108.56%, and the repeatability (expressed as the RSD) is between 4.66 and 8.90%. Graphical abstract The constructed DNA probes form a stable structure and bind to chloramphenicol specifically. One end of signal probes was labeled with the fluorophore 6-carboxyfluorescein (FAM). The detection sensitivity of chloramphenicol was significantly enhanced by using double signal amplification, which was superior to the traditional methods. The quantities of CAP can be achieved by fluorescence increment.

Nanomaterials in electrochemical cytosensors

Nano-electrochemical cytosensors have attracted intensive attention and achieved huge progress in the biomedical field owing to their stability, rapidity, accuracy, and low-cost properties.

Advances in functional nucleic acid based paper sensors

This article provides an extensive review of paper-based sensors that utilize functional nucleic acids, particularly DNA aptamers and DNAzymes, as recognition elements.

An ultrasensitive electrochemical cytosensor for highly specific detection of HL-60 cancer cells based on metal ion functionalized titanium phosphate nanospheres

Facile and sensitive detection methods of cancer cells in the early stage are beneficial for monitoring cancers and treating patients in time to reduce the death rate. In this work, an ultrasensitive cytosensor was constructed using aptamers as cell capturers and metal ion-exchanged titanium phosphate nanospheres as electrochemical probes. KH1C12 can specifically recognize HL-60 cells and distinguish them from other cell lines, K562 and CCRF-CEM, to obtain high selectivity. Cadmium ion functionalized titanium phosphate nanospheres show large quantities of electroactive cadmium ion output and a highly sensitive electrochemical signal. This proposed cytosensor showed a wide dynamic linear range from 102 cells per mL to 107 cells per mL with a low detection limit of 35 cells per mL, providing a new, simple and ultrasensitive platform for cancer diagnosis in biomedical and clinical research.

Optical transformation of a CdTe quantum dot-based paper sensor for a visual fluorescence immunoassay induced by dissolved silver ions

This work designs a visual fluorescence immunoassay for carcinoembryonic antigen based on structural and optical transformation of CdTe quantum dots immobilized on paper by cation-exchange reaction.

Versatile aptasensor for electrochemical quantification of cell surface glycan and naked-eye tracking glycolytic inhibition in living cells

Quantifying the glycan expression status on cell surfaces is of vital importance for insight into the glycan function in biological processes and related diseases. Here we developed a versatile aptasensor for electrochemical quantification of cell surface glycan by taking advantage of the cell-specific aptamer, and the lectin-functionalized gold nanoparticles acting as both a glycan recognition unit and a signal amplification probe. To construct the aptasensor, amine-functionalized mucin 1 protein (MUC1) aptamer was first covalently conjugated to carboxylated-magnetic beads (MBs) using the succinimide coupling (EDC-NHS) method. On the basis of the specific recognition between aptamer and MUC1 protein that overexpressed on the surface of MCF-7 cells, the aptamer conjugated MBs showed a predominant capability for cell capture with high selectivity. Moreover, a lectin-based nanoprobe was designed by noncovalent assembly of concanavalin A (ConA) on gold nanoparticles (AuNPs). This nanoprobe incorporated the abilities of both the specific carbohydrate recognition and the signal amplification based on the gold-promoted reduction of silver ions. By coupling with electrochemical stripping analysis, the proposed sandwich-type cytosensor showed an excellent analytical performance for the ultrasensitive detection of MCF-7 cells and quantification of cell surface glycan. More importantly, taking advantage of Con A-gold nanoprobe catalyzed silver enhancement, the proposed method was further used for naked-eye tracking glycolytic inhibition in living cells. This aptasensor holds great promise as a new point-of-care diagnostic tool for analyzing glycan expression on living cells and further helps cancer diagnosis and treatment.