Fast and sensitive smartphone colorimetric detection of whole blood samples on a paper-based analytical device

BACKGROUND

Methods based on paper-based analytical devices (PAD) and smartphone photographic colorimetric detection have become representative instrument-independent point-of-care testing (POCT) platforms due to their low cost and simplicity. However, the detection of target components from whole blood sample still presents challenges in terms of field preparation of small amounts of blood sample and detection sensitivity. This paper presents a rapid online processing method for whole blood samples on PAD based on plasma separation membrane (PSM), and combined with electrokinetic stacking and selective chromatic reaction. Real-time smartphone-based colorimetric detection of free hemoglobin (FHb) and human serum albumin (HSA) was successfully demonstrated.

RESULTS

With the proposed method, both detections for low and high concentration analytes could be implemented. The limits of detection of 16.6 mg L-1 for FHb and 0.67 g L-1 for HSA were obtained, respectively, with RSD below 8 %. The reliability of the method was verified by the recovery test and desktop spectrophotometric method. The detection results for real blood samples were in agreement with that by clinical methods.

SIGNIFICANCE AND NOVELTY

The PAD method is inexpensive, simple and fast, and detection of a whole blood sample of 5 μL can be finished in 5 min. This work shows that POCT of biomarkers from whole blood with PAD is possible without using any desktop facilities.

Cr speciation analysis based on electrokinetic sample pretreatment with a paper based analytical device

This work presents a new method of Cr speciation analysis based on micro sample pretreatment with a paper-based analytical device (PAD). By using electrokinetic separation and stacking on the PAD, Cr (VI) and Cr (III) can be separated and the recovered to achieve speciation analysis without have to be subjected to subtraction treatment. The separation and recovery properties of Cr (VI) and Cr (III) were characterized and optimized by UV-Vis spectrophotometry, with which the LOQ of 19.0 μg L^-1 and 28.7 μg L^-1, and the recoveries of 88-108% and 90-110%, were obtained for Cr (VI) and Cr (III), respectively. In addition, direct analysis of Cr (VI)/Cr (III) from an electroplating wastewater sample was also demonstrated with this method combined with atomic spectroscopy (GF-AAS and ICP-OES). This sample pretreatment method is fast, cheap and easy to be used. Combined with the high sensitivity and elemental selectivity of atomic spectroscopy and mass spectrometry, this PAD sample pretreatment method could be a compensation to their lack in speciation discrimination, and may play an important role in the speciation analysis of Cr.

Sensitive paper-based analytical device for fast colorimetric detection of nitrite with smartphone

On-site rapid monitoring of nitrite as an assessment indicator of the environment, food, and physiological systems has drawn extensive attention. Here, electrokinetic stacking (ES) was combined with colorimetric reaction on a paper-based device (PAD) to achieve colorless nitrite detection with smartphone. In this paper, nitrite was stacked on the paper fluidic channel as a narrow band by electrokinetic stacking. Then, Griess reagent was introduced to visualize the stacking band. Under optimal conditions, the sensitivity of nitrite was 160-fold increased within 5 min. A linear response in the range of 0.075 to 1.0 μg mL^-1 (R² = 0.99) and a limit of detection (LOD) of 73 ng mL^-1 (0.86 μM) were obtained. The LOD was 10 times lower than the reported PAD, and close to that achieved by a desktop spectrophotometer. The applicability was demonstrated by nitrite detection from saliva and water with good selectivity, adding 100 times more concentrated co-ions. High recovery (91.0~108.7%) and reasonable intra-day and inter-day reproducibility (RSD < 9%) were obtained. This work shows that the sensitivity of colorless analyte detection-based colorimetric reaction can be effectively enhanced by integration of ES on a PAD. Graphical abstract Schematic of the experimental setups (left) and the corresponding images (right) of the actual portable device.