Sensitive and simple multi-ion detection using organic nanocrystal enrichment in paper analytical devices

Microfluidic paper analytical devices (μPADs) are among the most promising platforms for heavy metal ion analysis. On the other hand, achieving simple and highly sensitive analysis of μPADs is challenging. In this study, we developed a simple enrichment method for sensitive multi-ion detection utilizing water-insoluble organic nanocrystals accumulated on μPAD. By combining the enrichment method with multivariate data analysis, three metal ion concentrations in the ion mixtures were simultaneously quantified with high sensitivity owing to the sensitive responses of the organic nanocrystals. In this work, we successfully quantified Zn²⁺, Cu²⁺, and Ni²⁺ at 20 ng L^-1 in the mixed ion solution using only two dye indicators with a larger sensitivity improvement than those reported in previous studies. Interference studies revealed possibilities for a practical application in real sample analysis. This developed approach also can be used for other analytes.

Disposable Paper-Based Biosensors for the Point-of-Care Detection of Hazardous Contaminations-A Review

The fast detection of trace amounts of hazardous contaminations can prevent serious damage to the environment. Paper-based sensors offer a new perspective on the world of analytical methods, overcoming previous limitations by fabricating a simple device with valuable benefits such as flexibility, biocompatibility, disposability, biodegradability, easy operation, large surface-to-volume ratio, and cost-effectiveness. Depending on the performance type, the device can be used to analyze the analyte in the liquid or vapor phase. For liquid samples, various structures (including a dipstick, as well as microfluidic and lateral flow) have been constructed. Paper-based 3D sensors are prepared by gluing and folding different layers of a piece of paper, being more user-friendly, due to the combination of several preparation methods, the integration of different sensor elements, and the connection between two methods of detection in a small set. Paper sensors can be used in chromatographic, electrochemical, and colorimetric processes, depending on the type of transducer. Additionally, in recent years, the applicability of these sensors has been investigated in various applications, such as food and water quality, environmental monitoring, disease diagnosis, and medical sciences. Here, we review the development (from 2010 to 2021) of paper methods in the field of the detection and determination of toxic substances.

Inkjet-printed paper-based sensor array for highly accurate pH sensing

In this work, a novel paper-based colorimetric sensor array was developed by inkjet printing method with polyethylene glycol (PEG) immobilization system. Eight commercially available pH indicators with sequential pH segments in nearly whole pH range were dissolved in nine mixed inks to fabricate the 3 × 3 sensor array on mixed cellulose ester (MCE) paper. Based on homogeneous deposition of inkjet printing, the eight pH indicators were sufficiently immobilized on MCE paper with the assistance of PEG-400, which guaranteed pH detection of aqueous samples on sensor array without hydrophobic barriers. Besides, the indicating range of each indicator obtained an extension through the addition of PEG 400, which remarkably enriched the distinguishable capability of sensor array and benefited for high resolution of pH detection. As such, the as-fabricated paper-based sensor array exhibited an excellent discrimination ability in pH range of 1.00-13.60 with a high resolution of 0.20 pH unit, not only for standard pH buffer solutions but for real aqueous samples.

Paper-Based Microfluidic Sensors for Onsite Environmental Detection: A Critical Review

A newly developed research topic, fabricated paper-based microfluidic sensors, was discussed in the field of low-cost environmental detection. Distinguished with the traditional dipstick or lateral-flow setups, these paper-based microfluidic sensors can serve as a tool for onsite quantitative and semi-quantitative measurements, without risks to cause environmental pollution. They have attracted increasing interest since the first easy-fabricated paper-based setup reported by Whitesides group in 2007. Most of the publications utilized paper-based sensors in clinical detection. In recent years, some groups started to use these sensors in environmental measurement, leading to precise, easy operation, low-cost, and eco-friendly methods for onsite detection. In this review, paper-based microfluidic sensors were briefly introduced, followed by literatures review and discussion for future perspectives.

A convenient and rapid method for detecting d-glucose in honey used smartphone

Information concerning food composition, including information on its glucose content, is essential for modern food industry due to greater consumer awareness and expectations. In this work, the gene encoding d-glucose dehydrogenase (GDH) from Bacillus Natto was expressed in Escherichia coli BL21(DE3) firstly. Ni-IDA column was used for the purification of GDH. Then, the purified GDH was used to construct a color system with stable and effective measurement of concentration of d-glucose. The smart phone photographing and the software Microsoft Photoshop have been used in the system for determination of the color. The enzymatic analysis system can detect the concentration of d-glucose from 5 mM to 40 mM, and other various sugars has no interference to the system. The system was used to quantitatively detect the concentration of d-glucose in honey. The system can be used for convenient and rapid detection of d-glucose in food, especially for large numbers of samples.

Tuning the anion binding properties of lanthanide receptors to discriminate nucleoside phosphates in a sensing array

The development of synthetic receptors for the selective binding and discrimination of anions in water requires an understanding of how anions interact with these synthetic receptors. Molecules designed to differentiate nucleoside phosphate anions (e.g. ATP, ADP, GTP, GDP, UDP) under physiological conditions could underpin exciting new sensing tools for biomedical research and drug discovery, but it is very challenging due to the similarities in anion structure, size and charge. We present a series of lanthanide-based anion receptors and establish key structural elements that impact on nucleoside phosphate anion binding and sensing. Structural evidence of anion binding using X-ray crystallographic and NMR data, supported by DFT calculations indicate the binding modes between the lanthanide complexes and certain phosphoanions, revealing a bidentate (α-, γ-) binding mode to ATP. We further use four of the receptors to allow discrimination of eight nucleoside phosphate anions in the first array-based assay using lanthanide complexes, taking advantage of the multiple emission bands and long emission lifetimes associated with luminescent lanthanide complexes.

Accessory-free quantitative smartphone imaging of colorimetric paper-based assays

The combination of smartphone technology and colorimetric paper-based microfluidics can enable simple, inexpensive diagnostics. However, imaging colorimetric diagnostic results via smartphones currently requires accessories to mitigate the influence of variability in surrounding lighting conditions. Here, we present an accessory-free smartphone-based colorimetric imaging method that enlists the built-in LED light source to dominate ambient lighting in combination with background and colour rescaling. This simple approach enables quantitative measurements from paper-based tests by compensating for different environmental lighting conditions and is universally applicable with respect to phone models and manufacturers. We demonstrate the method with three dominant phone makes and models in a cell counting application with a paper-based yeast detection device. The detection results are in good agreement with cell counting using automated cell counters. Eliminating the need for make/model specific accessories, this approach helps realize the potential for low-cost, broadly applicable paper-based diagnostics.

A Minimalist Approach for Distinguishing Individual Lanthanide Ions Using Multivariate Pattern Analysis

To discriminate among the 14 trivalent lanthanide ions, curcumin, a naturally occurring, nontoxic, off-the-shelf, commercially available compound containing a single fluorophore, was chosen as a probe in the water media at pH 6.8 and pH 8.2. By measuring the emission and absorption spectra of the probe, under the different pH conditions, and by performing linear discriminant analysis on the data, 14 Ln³⁺ ions were discriminated. Additionally, an easy tool for the nonspecialists was developed with easily available household substances, using a smartphone app, which added an extra advantage to this single probe. This probe possesses advantageous features in terms of low-cost and instant on-site detection of the lanthanide ions.

Quantitative colorimetric paper analytical devices based on radial distance measurements for aqueous metal determination

The On-Target test cards are a rapid testing method for untrained users to quantitatively assess contaminants in aqueous samples.

Fluorescent sensing arrays for cations and anions

A review of fluorescent sensing arrays for anions and cations, highlighting promising strategies and directions for future research.

New Functionalities for Paper-Based Sensors Lead to Simplified User Operation, Lower Limits of Detection, and New Applications

In the last decade, paper analytical devices (PADs) have evolved into sophisticated yet simple sensors with biological and environmental applications in the developed and developing world. The focus of this review is the technological improvements that have over the past five years increased the applicability of PADs to real-world problems. Specifically, this review reports on advances in sample processing, fluid flow control, signal amplification, and component integration. Throughout, we have sought to emphasize advances that retain the main virtues of PADs: low cost, portability, and simplicity.

Potential-Modulated Electrochemiluminescence of Carbon Nitride Nanosheets for Dual-Signal Sensing of Metal Ions

As an emerging semiconductor, graphite-phase polymeric carbon nitride (GPPCN) has drawn much attention not only in photocatalysis but also in optical sensors such as electrochemiluminescence (ECL) sensing of metal ions. However, when the concentrations of interfering metal ions are several times higher than that of the target metal ion, it is almost impossible to distinguish which metal ion changes the ECL signals in real sample detection. Herein, we report that the dual-ECL signals could be actuated by different ECL reactions merely from GPPCN nanosheets at anodic and cathodic potentials, respectively. Interestingly, the different metal ions exhibited distinct quenching/enhancement of the ECL signal at different driven potentials, presumably ascribed to the diversity of energy-level matches between the metal ions and GPPCN nanosheets and catalytic interactions of the intermediate species in ECL reactions. On this basis, without any labeling and masking reagents, the accuracy and reliability of sensors based on the ECL of GPPCN nanosheets toward metal ions were largely improved; thus, the false-positive result caused by interferential metal ions could be effectively avoided. As an example, the proposed GPPCN ECL sensor with a detection limit of 1.13 nM was successfully applied for the detection of trace Ni(2+) ion in tap and lake water.