Electrochemical sensor for the assessment of carbohydrate deficient transferrin: Application to diagnosis of congenital disorders of glycosilation

A dual colorimetric-electrochemical microfluidic paper-based analytical device for point-of-care testing of ischemic strokes

A novel microfluidic paper-based analytical device with dual colorimetric and electrochemical detection (dual μPAD) was developed for the assessment of transferrin saturation (TSAT) in samples from ischemic stroke patients. TSAT was calculated from the ratio between transferrin-bound iron, which was colorimetrically measured, and the total iron-binding capacity, which was electrochemically measured. To this end, a μPAD was smartly designed, which integrated both colorimetric and electrochemical detection reservoirs, communicating via a microchannel acting as a chemical reactor, and with preloading/storing capabilities (reagent-free device). This approach allowed the dual and simultaneous determination of both parameters, providing an improvement in the reliability of the results due to an independent signal principle and processing. The μPADs were validated by analyzing a certified reference material, showing excellent accuracy (Er ≤ 5%) and precision (RSD ≤ 2%). Then they were applied to the analysis of diagnosed serum samples from ischemic stroke patients. The results were compared to those provided by a free-interference method (urea-PAGE). Impressively, both methods exhibited a good correlation (r = 0.96, p < 0.05) and no significant differences were found between them (slope 1.0 ± 0.1 and the intercept 1 ± 4, p < 0.05), demonstrating the excellent accuracy of our approach during the analysis of complex samples from ischemic stroke patients, using just 90 μL of clinical samples and taking less than 90 min in comparison with the 18 hours required by the urea-PAGE approach. The developed fully integrated colorimetric-electrochemical μPAD is a promising ready to use reagent-free device for the point-of-care testing of TSAT, which can be used to assist physicians in the fast diagnosis and prognosis of ischemic strokes, where the decision-time is crucial for the patient's survival.

Paper-Based Analytical Devices for Accurate Assessment of Transferrin Saturation in Diagnosed Clinical Samples from Ischemic Stroke Patients

For the first time, a paper-based analytical device (PAD) was developed for the assessment of transferrin saturation (TSAT), which is defined as the ratio between iron bound to transferrin (Tf) and the total iron-binding capacity (TIBC) of Tf. Both parameters were simultaneously measured on the same PAD using ferrozine as a chromophore and a smartphone as the color reader. To this end, Tf was first isolated from serum using anti-Tf immunomagnetic beads to ensure that only the Tf-bound iron was measured, improving the selectivity and accuracy of TSAT assessment. To demonstrate the practical utility of the device, it was validated by analyzing a certified reference material, showing excellent accuracy (Er < 4%) and good precision (RSD ≤ 6%). Finally, 18 diagnosed serum samples from ischemic stroke patients were analyzed by this approach, and the results were compared with those obtained by urea-PAGE, showing not only an excellent correlation (r = 0.93, p < 0.05) but that the PAD approach has become statistically identical to the free-interference urea-PAGE. In comparison with the slow, tedious, and non-miniaturized-PAGE, this PAD approach exhibited attractive characteristics such as low cost, disposability, and connectivity, showing great potential for future point-of-care testing, especially in developing countries and/or remote areas, where access to medical or clinical facilities is limited.

Integrated calibration and serum iron in situ analysis into an array microfluidic paper-based analytical device with smartphone readout

In this work, a colorimetric microfluidic paper-based analytical device (μPAD) combined with a smartphone readout was proposed for the determination of serum iron (Fe³⁺), which is linked to transferrin. Firstly, Fe³⁺ was selectively isolated and preconcentrated from serum by using anti-transferrin immunomagnetic beads (anti-Tf-MBs). Secondly, Fe³⁺ is reduced to Fe²⁺ by a hydroxylamine solution (pH 4.8) and then measured in the μPAD, which contains the colorimetric reagent ferrozine. Finally, the intensity of the purple color formed in the μPAD was measured by a smartphone. The approach exhibited an excellent linear correlation (r = 0.996) and good limit of detection (0.3 μg mL^-1). Moreover, a certified reference material (human serum) was analyzed by this approach, showing an excellent accuracy (E_r < 4%) and inter-device reproducibility (RSD = 1%, n = 3). Interestingly, the μPAD array-design allowed the simultaneous analysis of different samples, improving the sample throughput (up to 5 samples in 130 min, using 100 μL each), and the integration of calibration and analysis into the same device, simplifying the analysis without losing accuracy or sensitivity, and avoiding inter-device variability, which constituted an added value to this approach. These disposable μPADs meet several requirements of point-of-care testing (POCT) because it is cheap, portable, easy-to-use, sensitive, and specific. Therefore, it may be an interesting way for measuring patients' serum iron levels in situ with reliability, especially, in developing countries, where the prevalence of iron deficiency and iron-deficiency anemia is higher and there are lower health resources than in developed countries.