Quantum Dot-Modified Paper-Based Assay for Glucose Screening

Low-tech vs. high-tech approaches in μPADs as a result of contrasting needs and capabilities of developed and developing countries focusing on diagnostics and point-of-care testing

Paper-based analysis has captivated scientists' attention in the field of analytical chemistry and related areas for the last two decades. Arguably no other area of modern chemical analysis is so broad and diverse in its approaches spanning from simple 'low-tech' low-cost paper-based analytical devices (PADs) requiring no or simple instrumentation, to sophisticated PADs and microfluidic paper-based analytical devices (μPADs) featuring elements of modern material science and nanomaterials affording high selectivity and sensitivity. Correspondingly diverse is the applicability, covering resource-limited scenarios on the one hand and most advanced approaches on the other. Herein we offer a view reflecting this diversity in the approaches and types of devices. The core idea of this article rests in dividing μPADs according to their type into two groups: A) instrumentation-free μPADs for resource-limited scenarios or developing countries and B) instrumentation-based μPADs as futuristic POC devices for e-diagnostics mainly aimed at developed countries. Each of those two groups is presented and discussed with the view of the main requirements in the given area, the most common targets, sample types and suitable detection approaches either implementing high-tech elements or low-tech low-cost approaches. Finally, a socioeconomic perspective is offered in discussing the fabrication and operational costs of μPADs, and, future perspectives are offered.

Portable Plasmonic Paper-Based Biosensor for Simple and Rapid Indirect Detection of CEACAM5 Biomarker via Metal-Enhanced Fluorescence

Rapid, simple, and sensitive analysis of relevant proteins is crucial in many research areas, such as clinical diagnosis and biomarker detection. In particular, clinical data on cancer biomarkers show great promise in forming reliable predictions for early cancer diagnostics, although the current analytical systems are difficult to implement in regions of limited recourses. Paper-based biosensors, in particular, have recently received great interest because they meet the criteria for point-of-care (PoC) devices; the main drawbacks with these devices are the low sensitivity and efficiency in performing quantitative measurements. In this work, we design a low-cost paper-based nanosensor through plasmonic calligraphy by directly drawing individual plasmonic lines on filter paper using a ballpoint pen filled with gold nanorods (AuNR) as the colloidal ink. The plasmonic arrays were further successively coated with negatively and positively charged polyelectrolyte layers employed as dielectric spacers to promote the enhancement of the emission of carboxyl-functionalized quantum dots (QD)—previously conjugated with specific antibodies—for indirect detection of the carcinoembryonic antigen-related cell adhesion molecule 5 (CEACAM5). The efficiency, sensitivity, as well as the specificity of our portable nanosensor were validated by recording the luminescence of the QD@Ab complex when different concentrations of CEACAM5 were added dropwise onto the calligraphed plasmonic arrays.

Portable and Intelligent Urine Glucose Analyzer Based on a CdTe QDs@GOx Aerogel Circular Array Sensor

Diabetes is a public health problem characterized by hyperglycemia, high mortality, and morbidity. A simple, rapid, and sensitive glucose detection method for diabetes screening and health self-management of patients with diabetes is of great significance. Therefore, an attractive urine glucose (UG) analyzer with advantages of fastness, sensitivity, and portability was developed. A cadmium telluride quantum dots (CdTe QDs)@glucose oxidase (GOx) aerogel circular array sensor can emit visible red fluorescence when excited by a 365 nm ultraviolet light source inside the analyzer. When urine samples containing glucose were dropped onto the sensor, glucose was oxidized by GOx to produce hydrogen peroxide (H₂O₂), which quenched the red fluorescence of CdTe QDs. The fluorescence images of the sensor were obtained using a CCD camera, and the linear relationship between the glucose concentration and the gray value of the fluorescence image was established. The analyzer shows good sensitivity (LOD, 0.12 mM) with a wide linear range of 0.12-26 mM. Based on the linear relation, the software of the analyzer was written in the C++ language, which can automatically give the gray value of the image and the corresponding glucose concentration. The UG analyzer was used for the detection of a large number clinical samples and compared with a variety of UG test papers, which all showed good detection performance. The novel analyzer we proposed has an important significance in the screening of diabetes and the self-management of diabetic patients.

Nanocellulose Films to Improve the Performance of Distance-based Glucose Detection in Paper-based Microfluidic Devices

We report on a simple, cost-effective, instrument-free, and portable distance-based paper device coupled with NFs for the determination of glucose. The analysis reaction is based upon the oxidative etching reaction of silver nanoparticles (AgNPs) in the presence of H₂O₂ that is produced from glucose after a glucose oxidase (GOx) catalytic reaction leading to a morphological transformation of AgNPs. A color band length of AgNPs is coated on to a detection channel and then etched by H₂O₂, and these were changed from a purple color to colorless as a correlate of the glucose concentration. To improve the performance of the enzyme immobilization, NFs, which are biocompatible without compromising their structure and biological activity, were then placed onto the sample zone. The naked-eye detection limit was 0.1 mM for 40 min of analysis time. The recoveries of glucose spiked in the artificial urine samples and control urine samples were then verified by our device and were in the acceptable range of 96 - 100%.

Affinity Immobilization of Semiconductor Quantum Dots and Metal Nanoparticles on Cellulose Paper Substrates

Colloidal semiconductor quantum dots (QDs), metal nanoparticles, and cellulose paper are materials with numerous applications in bioanalysis and beyond. The functional properties of QDs and metal NPs are substantially different than those of cellulose, such that their integration with cellulose paper is potentially enabling for many applications. Here, we characterize and evaluate multiple chemistries that modify cellulose paper substrates for the affinity-based immobilization of QDs, gold nanoparticles (Au NPs), and platinum nanoparticles (Pt NPs). These chemistries include grafting of cellulose fibers with imidazole and dithiol groups, as well as the aminosilanization of cellulose fibers (both with and without subsequent grafting with dithiol groups). Cellulose modifications and nanoparticle immobilization are characterized by multiple techniques, including, but not limited to, X-ray photoelectron spectroscopy, scanning electron microscopy, and optical imaging, extinction, and fluorescence measurements. We demonstrate the on-paper immobilization of color-tuned mixtures of QDs, on-paper patterning of QDs by microcontact printing, and post-immobilization enhancement of energy transfer and model assays of protease activity. The robustness of QD photoluminescence is also evaluated between immobilization chemistries. Paper-immobilized Au NPs and Pt NPs are evaluated as potential substrates for SERS and as supported catalysts for a model decolorization reaction. Our cumulative results indicate that there may not be a one-size-fits-all immobilization chemistry. Instead, the immobilization chemistry should be tailored and optimized for the downstream application.

A silver metal complex as a luminescent probe for enzymatic sensing of glucose in blood plasma and urine

In this work, we present a facile preparation of a paper-based glucose assay for rapid, sensitive, and quantitative measurement of glucose in blood plasma and urine. Two copper phosphorescent complexes [Cu(2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline)(2,6-dimethylphenylisocyanide)2][B(C6H3(CF3)2)4] (Cu1) and [Cu(2,9-dimethyl-1,10-phenanthroline)(2,6-dimethylphenylisocyanide)2][B(C6H3(CF3)2)4] (Cu2) and a new silver congener [Ag(P3)CNAg(P3)][B(C6H3(CF3)2)4] (Ag3) (P3 = PPh2C6H4-PPh-C6H4PPh2 [bis(o-diphenylphosphinophenyl)phenylphosphine]) have been synthesized and their oxygen sensing abilities were investigated. The dimetallic phosphine-based Ag3 complex, having a high oxygen sensing ability, was employed as an efficient signal transducer in enzymatic reactions to recognize blood plasma glucose and urine glucose, which provided a wide linear response for a concentration range between 1.0 and 35 mM and a rapid response, with a limit of detection (LOD) of 0.09 mM for glucose. In practical application, this Ag3 paper-based device offers great analytical reliability and accuracy upon monitoring glucose concentrations in blood plasma.

Biosensing strategies based on enzymatic reactions and nanoparticles

Application of new nanomaterials to detection of enzymatic activities allows the development of new sensitive and selective bioanalytical assays based on enzymes for recognition and signal amplification.

Non-enzymatic electrochemical detection of glucose with a disposable paper-based sensor using a cobalt phthalocyanine-ionic liquid-graphene composite

We introduce for the first time a paper-based analytical device (PAD) for the non-enzymatic detection of glucose by modifying a screen-printed carbon electrode with cobalt phthalocyanine, graphene and an ionic liquid (CoPc/G/IL/SPCE). The modifying composite was characterized by UV-visible spectroscopy, energy dispersive X-ray spectroscopy (EDX), transmission electron microscopy (TEM) and scanning electron microscopy (SEM). The disposable devices show excellent conductivity and fast electron transfer kinetics. The results demonstrated that the modified electrode on PADs had excellent electrocatalytic activity towards the oxidation of glucose with NaOH as supporting electrolyte (0.1M). The oxidation potential of glucose was negatively shifted to 0.64V vs. the screen-printed carbon pseudo-reference electrode. The paper-based sensor comprised a wide linear concentration range for glucose, from 0.01 to 1.3mM and 1.3-5.0mM for low and high concentration of glucose assay, respectively, with a detection limit of 0.67µM (S/N = 3). Additionally, the PADs were applied to quantify glucose in honey, white wine and human serum. The disposable, efficient, sensitive and low-cost non-enzymatic PAD has great potential for the development of point-of-care testing (POCT) devices that can be applied in healthcare monitoring.

Analysis of penicillamine using Cu-modified graphene quantum dots synthesized from uric acid as single precursor

A simple methodology was developed to quantify penicillamine (PA) in pharmaceutical samples, using the selective interaction of the drug with Cu-modified graphene quantum dots (Cu-GQDs). The proposed strategy combines the advantages of carbon dots (over other nanoparticles) with the high affinity of PA for the proposed Cu-GQDs, resulting in a significant and selective quenching effect. Under the optimum conditions for the interaction, a linear response (in the 0.10–7.50 µmol/L PA concentration range) was observed. The highly fluorescent GQDs used were synthesized using uric acid as single precursor and then characterized by high resolution transmission electron microscopy, Raman spectroscopy, X-ray diffraction, Fourier transform infrared spectroscopy, fluorescence, and absorption spectroscopy. The proposed methodology could also be extended to other compounds, further expanding the applicability of GQDs.

A Review on Microfluidic Paper-Based Analytical Devices for Glucose Detection

Glucose, as an essential substance directly involved in metabolic processes, is closely related to the occurrence of various diseases such as glucose metabolism disorders and islet cell carcinoma. Therefore, it is crucial to develop sensitive, accurate, rapid, and cost effective methods for frequent and convenient detections of glucose. Microfluidic Paper-based Analytical Devices (μPADs) not only satisfying the above requirements but also occupying the advantages of portability and minimal sample consumption, have exhibited great potential in the field of glucose detection. This article reviews and summarizes the most recent improvements in glucose detection in two aspects of colorimetric and electrochemical μPADs. The progressive techniques for fabricating channels on μPADs are also emphasized in this article. With the growth of diabetes and other glucose indication diseases in the underdeveloped and developing countries, low-cost and reliably commercial μPADs for glucose detection will be in unprecedentedly demand.

Synthesis of CuNP-Modified Carbon Electrodes Obtained by Pyrolysis of Paper

A one-step approach for the synthesis and integration of copper nanoparticles (CuNPs) onto paper-based carbon electrodes is herein reported. The method is based on the pyrolysis (1000 °C under a mixture of 95% Ar / 5% H₂ for 1 hour) of paper strips modified with a saturated solution of CuSO₄ and yields to the formation of abundant CuNPs on the surface of carbonized cellulose fibers. The resulting substrates were characterized by a combination of scanning electron microscopy, EDX, Raman spectroscopy as well as electrical and electrochemical techniques. Their potential application, as working electrodes for nonenzymatic amperometric determination of glucose, was then demonstrated (linear response up to 3 mM and a sensitivity of 460 ± 8 μA·cm^-2·mM^-1). Besides being a simple and inexpensive process for the development of electrochemically-active substrates, this approach opens new possibilities for the in-situ synthesis of metallic nanoparticles without the traditional requirements of solutions and adjuvants.