Paper microfluidic device using carbon dots to detect glucose and lactate in saliva samples.

Bioanalyses are commonly performed with blood or serum samples. However, these analyses often require invasive and painful blood collection using a needle or finger pricking. Saliva is an alternative and very attractive biological medium for performing clinical analyses, since it contains many types of clinically relevant biomarkers and compounds. Its collection is straightforward and can be achieved in a non-invasive and stress-free way. However, the analytes are frequently present at low concentrations, while the viscosity of whole saliva hinders its analysis using paper devices, especially those with multiple layers (3D-µPADs). This work explores the use of a simple, fast, and low-cost saliva sample pretreatment using a cotton-paper-syringe filtration system, allowing the analysis of saliva samples using multilayer paper devices. The proposed methodology employs the oxidation of glucose and lactate, catalyzed by specific oxidase enzymes, producing hydrogen peroxide. The detection is based on the fluorescence quenching of carbon dots in the presence of hydrogen peroxidase. The concentrations of the analytes showed good linear correlations with the fluorescence quenching, with LODs of 2.60 × 10-6 and 8.14 × 10-7 mol L-1 for glucose and lactate, respectively. The proposed method presented satisfactory intra-day and inter-day repeatabilities, with %RSD values in the range 3.82-6.61%. The enzymatic systems proved to be specific for the analytes and the matrix had no significant influence on the glucose and lactate determinations. The proposed methodology was successfully applied to saliva and serum samples and was validated using certified material.

Direct Analysis of Doping Agents in Raw Urine Using Hydrophobic Paper Spray Mass Spectrometry.

In this study, the direct analysis of doping agents in urine samples with no sample preparation by a modified paper spray mass spectrometry (PS-MS) methodology has been demonstrated for the first time. We have described a paper surface treatment with trichloromethylsilane using a gas-phase reaction to increase the ionization of target compounds. This approach was applied for the analysis of two classes of banned substances in urine samples: anabolic agents (trenbolone and clenbuterol) and diuretics (furosemide and hydrochlorothiazide). Under optimized conditions, the developed methods presented satisfactory repeatability, and an analysis of variance showed linearity without lack-of-fit. Highly sensitive detections as low as sub-nanogram per milliliter levels, which is below the minimum required performance levels proposed by the World Anti-Doping Agency, have been reached using the hydrophobic PS-MS analysis without any preconcentration and cleanup step.

Bioactive paper platform for detection of hydrogen peroxide in milk.

This paper describes the development and application of a paper-based analytical device (µPAD) for the determination of hydrogen peroxide, an important adulterant in milk. The method employs the reaction between hydrogen peroxide and guaiacol, catalyzed by peroxidase, producing a red product, which is then quantified by digital imaging. Experimental design methodology was used to optimize the experimental conditions. The linear concentration range was from 12.5 × 10-4 to 150 × 10-4 mol L-1, resulting in the regression equation AB = 0.02466 (±0.00192) + 17.053 (±0.750) C, with an excellent correlation coefficient (r = 0.986). The relative standard deviations obtained were 1.1 and 1.3% (intra-day), and 4.8 and 2.9% (inter-day), for 25.0 × 10-4 and 100 × 10-4 mol L-1 of hydrogen peroxide, respectively. The limits of detection and quantification were 3.54 × 10-4 and 11.8 × 10-4 mol L-1, respectively, with standard deviation of the blank of 0.002012. The proposed method was successfully applied for the determination of peroxide in milk samples, with recoveries between 92.2 and 109%. The proposed device constitutes a valuable analytical tool for the identification of hydrogen peroxide adulteration and offers advantages including low cost, simplicity, portability, and no (or minimal) requirement for sample pretreatment.

Green synthesis of fluorescent carbon dots for determination of glucose in biofluids using a paper platform.

In this paper, we describe a novel carbon dot (CD) synthesized from citric acid and tyramine using a one-step microwave heating route. Under UV irradiation, the CD displayed blue emission that was quenched in the presence of H2O2 and peroxidase. This property was used to quantify glucose in biological samples, using a standard additions procedure employing a paper platform and the H2O2 formed in the enzymatic reaction with glucose oxidase. The attractive features of the paper platform include low cost, easy availability, biocompatibility, and hydrophilicity. The standard additions calibration method has the advantages that it can be performed using a single device, eliminates the need for external calibration, and reduces matrix effects associated with the sample and/or non-uniformity of the paper. The method developed was applied in the analysis of certified serum and urine samples. There were no statistically significant differences between the certified concentrations and the results obtained using the paper device with standard additions (Student's t-test at 95% confidence level).

A paper platform for colorimetric determination of aluminum hydrochloride in antiperspirant samples.

A simple, fast, low-cost, portable, and eco-friendly method using a spot test on a paper platform, together with diffuse reflectance spectroscopy, was developed and validated for the quantification of aluminum hydrochloride, a potential neurotoxic agent, in antiperspirant samples. The determination of aluminum hydrochloride was performed at a wavelength of 615 nm, by measuring consumption of the purple colorimetric reagent Alizarin S, due to reaction with aluminum. The linear range was from 10.0 to 125.0 mg L-1 and could be described by the equation: AR = 0.4479 - 0.002543 CAl (R = 0.999). The limits of detection (LOD) and quantification (LOQ) were 3.06 and 10.2 mg L-1, respectively. The method was specific, accurate, and repeatable, with relative standard deviation (RSD) <5.0%. The recovery was between 92.2 and 103.4%. The method was successfully used for the determination of aluminum hydrochloride in commercial antiperspirant samples, revealing concentrations below the maximum permitted by current legislation.

Simultaneous determination of renal function biomarkers in urine using a validated paper-based microfluidic analytical device.

In this paper, we describe a validated paper-based microfluidic analytical device for the simultaneous quantification of two important biomarkers of renal function in urine. This paper platform provides an inexpensive, simple, and easy to use colorimetric method for the quantification of creatinine (CRN) and uric acid (UA) in urine samples. The microfluidic paper-based analytical device (µPAD) consists of a main channel with three identical arms, each containing a circular testing zone and a circular uptake zone. Creatinine detection is based on the Jaffé reaction, in which CRN reacts with picrate to form an orange-red product. Uric acid quantification is based on the reduction of Fe3+ to Fe2+ by UA, which is detected in a colorimetric reaction using 1,10-phenanthroline. Under optimum conditions, obtained through chemometrics, the concentrations of the analytes showed good linear correlations with the effective intensities, and the method presented satisfactory repeatability. The limits of detection and the linear ranges, respectively, were 15.7 mg L-1 and 50-600 mg L-1 for CRN and 16.5 mg L-1 and 50-500 mg L-1 for UA. There were no statistically significant differences between the results obtained using the µPAD and a chromatographic comparative method (Student's t-test at 95% confidence level).