An electrochemical molecularly imprinted microfluidic paper-based chip for detection of inflammatory biomarkers IL-6 and PCT

Based on surface biomolecular imprinting technology, a rotary microfluidic electrochemical paper-based chip (MIP-ePADs) was proposed for sensitive and selective detection of human interleukin 6 (IL-6) and procalcitonin (PCT). Compared with the traditional method, the sample can be added directly on the MIP-ePAD by rotating the working electrode, which avoids the loss of the liquid to be tested and greatly simplifies the process of electropolymerization imprinting and template elution. Our experimental results show that linear concentration ranges of IL-6 and PCT in the electrochemical molecularly imprinted microfluidic paper-based chip ranged from 0.01 to 5 ng mL-1, with their detection limits being 3.5 and 2.1 pg mL-1, respectively. For the detection of actual serum samples, there was no significant difference between the results of MIP-ePADs and the traditional electrochemiluminescence method used in hospitals, indicating that the paper-based chip can be used for stable and accurate analysis and detection. The chip greatly reduces the cost of clinical trials due to its advantages of easy preparation and low cost. The chip can be used for the analysis of non-antibody inflammation markers and can be widely used in home and hospital treatment detection. This method will not only play an important role in rapid detection, but also provide new ideas for the improvement of rapid detection technology.

Paper-Based Molecular-Imprinting Technology and Its Application

Paper-based analytical devices (PADs) are highly effective tools due to their low cost, portability, low reagent accumulation, and ease of use. Molecularly imprinted polymers (MIP) are also extensively used as biomimetic receptors and specific adsorption materials for capturing target analytes in various complex matrices due to their excellent recognition ability and structural stability. The integration of MIP and PADs (MIP-PADs) realizes the rapid, convenient, and low-cost application of molecular-imprinting analysis technology. This review introduces the characteristics of MIP-PAD technology and discusses its application in the fields of on-site environmental analysis, food-safety monitoring, point-of-care detection, biomarker detection, and exposure assessment. The problems and future development of MIP-PAD technology in practical application are also prospected.

Molecularly Imprinted Polymer-Based Sensors for Priority Pollutants

Globally, there is growing concern about the health risks of water and air pollution. The U.S. Environmental Protection Agency (EPA) has developed a list of priority pollutants containing 129 different chemical compounds. All of these chemicals are of significant interest due to their serious health and safety issues. Permanent exposure to some concentrations of these chemicals can cause severe and irrecoverable health effects, which can be easily prevented by their early identification. Molecularly imprinted polymers (MIPs) offer great potential for selective adsorption of chemicals from water and air samples. These selective artificial bio(mimetic) receptors are promising candidates for modification of sensors, especially disposable sensors, due to their low-cost, long-term stability, ease of engineering, simplicity of production and their applicability for a wide range of targets. Herein, innovative strategies used to develop MIP-based sensors for EPA priority pollutants will be reviewed.

Molecularly imprinted polymer-enhanced biomimetic paper-based analytical devices: A review

The popularization of paper-based analytical devices (PADs) in analytical science has fostered research on enhancing their analytical performance for accurate and sensitive assays. With their superb recognition capability and structural stability, molecularly imprinted polymers (MIPs) have been extensively employed as biomimetic receptors for capturing target analytes in various complex matrices. The integration of MIPs as recognition elements with PADs (MIP-PADs) has opened new opportunities for advanced analytical devices with elevated selectivity and sensitivity, as well as a shorter assay time and a lower cost. This review covers recent advances in MIP-PAD fabrication and engineering based on multifarious signal transduction systems such as colorimetry, fluorescence, electrochemistry, photoelectrochemistry, and chemiluminescence. The application of MIP-PADs in the fields of biomedical diagnostics, environmental analysis, and food safety monitoring is also reviewed. Further, the advantages, challenges, and perspectives of MIP-PADs are discussed.

Perfluorooctanesulfonic Acid Detection Using Molecularly Imprinted Polyaniline on a Paper Substrate

Perfluorinated compounds like perfluorooctanesulfonic acid (PFOS) are synthetic water pollutants and have accumulated in environments for decades, causing a serious global health issue. Conventional assays rely on liquid chromatography and mass spectroscopy that are very expensive and complicated and thus limit the large-scale monitoring of PFOS in wastewater. To achieve low-cost and accurate detection of PFOS, we designed a paper-based sensor with molecularly imprinted polyaniline electrodes that have recognition sites specific to PFOS. The calibration curve of resistivity ratios as a function of PFOS concentrations has a linear range from 1 to 100 ppt with a coefficient of determination of 0.995. The estimated limit of detection is 1.02 ppt. We also investigated attenuated total reflectance Fourier-transform infrared spectroscopy (ATR-FTIR) and X-ray photoelectron spectroscopy (XPS) spectra of the surface of the polyaniline (PANI) electrodes to propose the potential recognition sites in polyaniline matrix and the detection mechanism. This electrical paper sensor with low cost and excellent sensitivity and selectivity provides the potential for large-scale monitoring of wastewater.

Non-enzymatic lactose molecularly imprinted sensor based on disposable graphite paper electrode

Lactose (LAC) is a disaccharide - major sugar, present in milk and dairy products. LAC content is an important indicator of milk quality and abnormalities in food industries, as well as in human and animal health. The present study reports the development of an innovative imprinted voltammetric sensor for sensitive detection of LAC. The sensor was constructed using electropolymerized pyrrole (Py) molecularly imprinted polymer (MIP) on graphite paper electrode (PE). The MIP film was constructed through the electrosynthesis of polypyrrole (PPy) in the presence of LAC (template molecule) on PE (PPy/PE). To optimize the detection conditions, several factors affecting the PPy/PE sensor performance were assessed by multivariate methods (Plackett-Burman design and central composite design). Under optimized conditions, the proposed analytical method was applied for LAC detection in whole and LAC-free milks, where it demonstrated high sensitivity and selectivity, with two dynamic linear ranges of concentration (1.0-10 nmol L^-1 and 25-125 nmol L^-1) and a detection limit of 0.88 nmol L^-1. The MIP sensor showed selective molecular recognition for LAC in the presence of structurally related molecules. The proposed PPy/PE sensor exhibited good stability, as well as excellent reproducibility and repeatability. Based on the results obtained, the PPy/PE is found to be highly promising for sensitive detection of LAC.

Engineering strategies for enhancing the performance of electrochemical paper-based analytical devices

Applications of electrochemical detection methods in microfluidic paper-based analytical devices (μPADs) has revolutionized the area of point-of-care (POC) testing towards highly sensitive and selective quantification of various (bio)chemical analytes in a miniaturized, low-coat, rapid, and user-friendly manner. Shortly after the initiation, these relatively new modulations of μPADs, named as electrochemical paper-based analytical devices (ePADs), gained widespread popularity within the POC research community thanks to the inherent advantages of both electrochemical sensing and usage of paper as a suitable substrate for POC testing platforms. Even though general aspects of ePADs such as applications and fabrication techniques, have already been reviewed multiple times in the literature, herein, we intend to provide a critical engineering insight into the area of ePADs by focusing particularly on the practical strategies utilized to enhance their analytical performance (i.e. sensitivity), while maintaining the desired simplicity and efficiency intact. Basically, the discussed strategies are driven by considering the parameters potentially affecting the generated electrochemical signal in the ePADs. Some of these parameters include the type of filter paper, electrode fabrication methods, electrode materials, fluid flow patterns, etc. Besides, the limitations and challenges associated with the development of ePADs are discussed, and further insights and directions for future research in this field are proposed.

Exploring Matrix Effects on Binding Properties and Characterization of Cotinine Molecularly Imprinted Polymer on Paper-Based Scaffold

Commercially available sorbent materials for solid-phase extraction are widely used in analytical laboratories. However, non-selective binding is a major obstacle for sample analysis. To overcome this problem, molecularly imprinted polymers (MIPs) were used as selective adsorbent materials prior to determining target analysts. In this study, the use of non-covalent molecularly imprinted polymers (MIPs) for cotinine adsorption on a paper-based scaffold was studied. Fiberglass paper was used as a paper scaffold for cotinine-selective MIP adsorption with the use of 0.5% agarose gel. The effects of salt, pH, sample matrix, and solvent on the cotinine adsorption and extraction process were investigated. Under optimal conditions, the adsorption isotherm of synthesized MIPs increased to 125.41 µg/g, whereas the maximum adsorption isotherm of non-imprinted polymers (NIPs) was stable at 42.86 µg/g. The ability of the MIP paper scaffold to absorb cotinine in water medium was approximately 1.8–2.8-fold higher than that of the NIP scaffold. From Scatchard analysis, two dissociation constants of MIPs were calculated to be 2.56 and 27.03 µM. Nicotine, myosmine, and N-nitrosonornicotine were used for selectivity testing, and the calculated selectivity factor of cotinine to nicotine, myosmine, and N-nitrosonornicotine was 1.56, 2.69, and 2.05, respectively. Overall, the MIP paper scaffold is promising for simple onsite sampling of cotinine and can be used to assess tobacco smoke exposure.

Recent advances in and potential utilities of paper-based electrochemical sensors: beyond qualitative analysis

Paper based electrochemical sensors (PESs) are simple, low-cost, portable and disposable analytical sensing platforms that can be applied in clinical diagnostics, food quality control and environmental monitoring.

Nanomaterials-modified cellulose paper as a platform for biosensing applications

Recently, paper substrates have attracted tremendous interest from both academia and industry. Not only is paper highly abundant and portable, it is lightweight, disposable, easy-to-use, and can be rolled or folded into 3D configurations. More importantly, with a unique porous bulk structure and rough and absorptive surface properties, the construction of nanomaterials-functionalized cellulose has enabled cellulose paper to be applied for point-of-care (POC) paper devices with reasonably good performance at low cost. In this review, the latest advances in the modification of nanomaterials on paper cellulose are summed up. To begin with, the attractive properties of paper-based analytical devices are described. Then, fabricating methods for the functionalization of cellulose with diverse materials, including noble metals, bimetals, metal oxides, carbon nanomaterials, and molecular imprinting polymer nanoparticles, as well as their applications, are introduced in detail. Finally, the current critical issues, challenges, and future prospectives for exploring a paper-based analytical system based on nanomaterials-modified cellulose are discussed. It is believed that more strategies will be developed in the future to construct nanomaterials-functionalized cellulose, paving the way for the mass production of POC paper devices with a satisfactory performance.

Imprinting Technology in Electrochemical Biomimetic Sensors

Biosensors are a promising tool offering the possibility of low cost and fast analytical screening in point-of-care diagnostics and for on-site detection in the field. Most biosensors in routine use ensure their selectivity/specificity by including natural receptors as biorecognition element. These materials are however too expensive and hard to obtain for every biochemical molecule of interest in environmental and clinical practice. Molecularly imprinted polymers have emerged through time as an alternative to natural antibodies in biosensors. In theory, these materials are stable and robust, presenting much higher capacity to resist to harsher conditions of pH, temperature, pressure or organic solvents. In addition, these synthetic materials are much cheaper than their natural counterparts while offering equivalent affinity and sensitivity in the molecular recognition of the target analyte. Imprinting technology and biosensors have met quite recently, relying mostly on electrochemical detection and enabling a direct reading of different analytes, while promoting significant advances in various fields of use. Thus, this review encompasses such developments and describes a general overview for building promising biomimetic materials as biorecognition elements in electrochemical sensors. It includes different molecular imprinting strategies such as the choice of polymer material, imprinting methodology and assembly on the transduction platform. Their interface with the most recent nanostructured supports acting as standard conductive materials within electrochemical biomimetic sensors is pointed out.

A molecularly imprinted polymer based a lab-on-paper chemiluminescence device for the detection of dichlorvos

In this work, a new molecularly imprinted polymer (MIP) based lab-on-paper device with chemiluminescence (CL) detection of dichlorvos (DDV) was designed. With the circle-shaped device, the MIP layer with certain depth was synthesized and adsorbed on the paper surface and DDV can be selectively imprinted on it. The adsorption and washing procedures can be achieved well on the paper-based chip. The paper-based device was fabricated by a simple cutting method and many chips can be made at the same time. On the basis of DDV enhancing CL of luminol-H2O2 greatly, the proposed MIP based lab-on-paper CL device showed better selectivity to DDV and it has been applied to the determination of DDV in vegetables in the range of 3.0 ng/mL-1.0 μg/mL with the detection limit of 0.8 ng/mL. This study has made a successful attempt in the development of highly selective and sensitive monitoring of DDV in real samples and will provide a new approach for sensitive and specific assay in environmental monitoring.

Growth of gold-manganese oxide nanostructures on a 3D origami device for glucose-oxidase label based electrochemical immunosensor

Flexible biosensors are of considerable current interest for the development of portable point-of-care medical products, minimally invasive implantable devices, and compact diagnostic platforms. Here, we reported an electrochemical paper based analytical device fabricated (EPADs) by sequentially growing gold nanoparticles (AuNPs) and manganese oxide (MnO2) nanowires networks on a freestanding three dimensional (3D) origami device. This fabricated through the growth of an AuNPs layer on the surfaces of cellulose fibers in the screen-printed paper working electrode (PWE), and thus developed a gold paper working electrode (Au-PWE). Subsequently, MnO2 nanowires were successfully electrodeposited on Au-PWE to form a 3D network with large surface areas. Based on this novel EPADs and the principle of origami, we presented herein a simple immunosensing scheme using glucose oxidase (GOx) as an enzyme label, 3,3',5,5'-tetramethylbenzidine (TMB) as a redox terminator, and glucose as an enzyme substrate. The electrochemical enzymatic redox cycling was applied to the detection of prostate protein antigen (PSA), a biomarker of prostatic cancer. The proposed method successfully fulfilled the highly sensitive detection of PSA with a linear range of 0.005 ng mL(-1)-100 ng mL(-1) with a detection limit of 0.0012 ng mL(-1). This EPADs exhibited high sensitivity, specificity and excellent performance in real human serum assay, and could be applied in point-of-care testing of other tumor markers for remote regions and developing countries.

Intelligent recognitive systems in nanomedicine

There is a bright future in the development and utilization of nanoscale systems based on intelligent materials that can respond to external input providing a beneficial function. Specific functional groups can be incorporated into polymers to make them responsive to environmental stimuli such as pH, temperature, or varying concentrations of biomolecules. The fusion of such "intelligent" biomaterials with nanotechnology has led to the development of powerful therapeutic and diagnostic platforms. For example, targeted release of proteins and chemotherapeutic drugs has been achieved using pH-responsive nanocarriers while biosensors with ultra-trace detection limits are being made using nanoscale, molecularly imprinted polymers. The efficacy of therapeutics and the sensitivity of diagnostic platforms will continue to progress as unique combinations of responsive polymers and nanomaterials emerge.