Paper-based analytical device with colorimetric detection for urease activity determination in soils and evaluation of potential inhibitors.

Urease is an enzyme associated with the degradation of urea, an important nitrogen fertilizer in agriculture. Thus, this current report describes the use of a paper-based analytical device (UrePAD) designed to contain a microzone array for colorimetric determination of urease activity in soils in the absence/presence of potential enzyme inhibitors. The UrePAD can be used at the point-of-need (point-of-care), and it offers advantages such as low cost, simplicity in handling, low sample/reagent volumes, and no use of toxic reagents. The acid-base indicator phenol red was used to monitor the urea hydrolysis reaction catalyzed by urease in the evaluated systems. The images were digitalized in a bench scanner, and the analysis was performed using Corel Draw X8 software. The device offered a LOD of 0.10 U mL-1 with linearity between 0.25 and 4.0 U mL-1 and a relative standard deviation ≤ 1.38%. UrePAD was tested in four soil samples of different characteristics and with eight urease inhibitors of varied classes. The results obtained through the proposed device did not differ statistically (95% confidence interval) from those employing the classic method based on the Berthelot reaction, thus indicating that UrePAD was effective for determining urease activity and screening inhibitors, besides showing the capacity to simplify fieldwork involving the application of urea in the soil.

Microfluidic toner-based analytical devices: disposable, lightweight, and portable platforms for point-of-care diagnostics with colorimetric detection.

This chapter describes the development of microfluidic toner-based analytical devices (µTADs) to perform clinical diagnostics using a scanner or cell-phone camera. µTADs have been produced in a platform composed of polyester and toner by the direct-printing technology (DPT) in a matter of minutes. This technology offers simplicity and versatility, and it does not require any sophisticated instrumentation. Toner-based devices integrate the current generation of disposable analytical devices along paper-based chips. The cost of one µTAD has been estimated to be lower than $0.10. In addition, these platforms are lightweight and portable thus enabling their use for point-of-care applications. In the last 5 years, great efforts have been dedicated to spread out the use of µTADs in bioassays. The current chapter reports the fabrication of printed microplates and integrated microfluidic toner-based devices for dengue diagnostics and rapid colorimetric assays with clinically relevant analytes including cholesterol, triglycerides, total proteins, and glucose. The use of µTADs associated with cell-phone camera may contribute to the health care, in special, to people housed in developing regions or with limited access to clinics and hospitals.

Laser-printing of toner-based 96-microzone plates for immunoassays.

This work describes the quick and simple fabrication of toner-based 96-microzone plates by a direct-printing technology. The printer deposits a toner layer (ca. 5 µm thick) on the polyester surface which acts as a hydrophobic barrier to confine small volumes of sample on test zones (wells). A 96-microzone toner plate was explored to demonstrate its capability of performing enzyme-linked immunosorbent assay (ELISA). The detection of anti-immunoglobulin G (anti-IgG) and immunoglobulin M (IgM) antibodies has been successfully achieved in cell culture and serum samples, respectively. The use of a conventional microplate reader has allowed obtaining a limit of detection of 13 fmol of mouse IgG per zone on printed microplates. The IgM antibody has been detected in a serum sample collected from a patient infected with dengue virus. The detection of a primary infection has been provided by a microplate reader and also by a cell phone camera. Besides the bioanalytical feasibility, toner-based zones have shown good repeatability for inter-zone and intra-plate comparisons. The relative standard deviation (RSD) values for inter-zone (n = 12) and intra-plate (n = 3) comparisons were lower than 6% and 11%, respectively. Furthermore, it was found that the lifetime of each printed microplate depends on the storage temperature. The shelf life for devices stored at 10 °C has been estimated to be ca. four weeks.