Additive manufacturing, also known as 3D-printing, is receiving great interest by chemists due to the easy design of novel materials, fast prototyping and reducing waste, which enables large-scale fabrication of electrochemical devices. Herein we demonstrate the development of (bio)sensors for the analysis of biological fluids using 3D-printing. Fused deposition modelling was used to fabricate (bio)sensing platforms from commercially-available filaments made of polylactic acid containing graphene (G-PLA). An enzymatic glucose biosensor fabricated on the G-PLA surface was developed and applied for glucose sensing in blood plasma using chronoamperometry. Oxygenated groups from the polymeric matrix provides suitable condition to enzyme immobilization by crosslinking with glutaraldehyde. The biosensor presented a limit of detection (LOD) of 15 μmol L−1, inter-day and intra-day precision lower than 5 %, and adequate recovery values (90–105 %) for the analysis of plasma. We also show that the surface treatment of the 3D-printed sensor (mechanical polishing followed solvent immersion) provides improved electrochemical properties for the direct detection of nitrite and uric acid. Differential-pulse voltammetry and multiple-pulse amperometry under flow conditions were evaluated and compared for the determination of both species in saliva and urine. Highlights are presented for the amperometric detection within a linear range from 0.5–250 μmol L−1 for both analytes, LODs of 0.02 and 0.03 μmol L−1 for uric acid and nitrite, respectively, and high precision (RSD

3D-Printed graphene/polylactic acid electrode for bioanalysis: Biosensing of glucose and simultaneous determination of uric acid and nitrite in biological fluids

Microfluidic paper-based analytical devices (μPADs) have experienced rapid growth over the past decade due to their simple design, low cost, minimal sample requirement, and good sensitivity, selectivity and accuracy. While designed originally for point-of-care medical diagnostics, biological, and food safety applications, μPADs are now used increasingly for environmental monitoring purposes. This review provides a detailed overview of the μPADs developed over the past ten years for the environmental analysis of soil, air, ecology (pesticides) and river water. The review commences by introducing the fabrication techniques and detection methods used in μPAD technology. A detailed description of the main μPAD frameworks proposed in the past decade for environmental monitoring is then provided. The review concludes by examining the challenges facing μPADs for environmental monitoring and identifying probable avenues of future research.

Microfluidic paper-based analytical devices for environmental analysis of soil, air, ecology and river water

Microfluidic paper-based devices (μPADs) and wearable devices have been highly studied to be used as diagnostic tools due to their advantages such as simplicity and ability to provide instrument-free fast results. Diseases such as periodontitis and diabetes mellitus can potentially be detected through these devices by the detection of important biomarkers. This study describes the development of μPADs through craft cutter printing for glucose and nitrite salivary diagnostics. In addition, the use of μPADs integrated into a mouthguard as a wearable sensor for glucose monitoring is also presented. μPADs were designed to contain two detection zones for glucose and nitrite assays and a sampling zone interconnected by microfluidic channels. Initially, the analytical performance of the proposed μPADs was investigated and it provided linear behavior (r2 ≥ 0.994) in the concentration ranges between 0 to 2.0 mmol L−1 and 0 to 400 μmol L−1 for glucose and nitrite, respectively. Under the optimized conditions, the limits of detection achieved for glucose and nitrite were 27 μmol L−1 and 7 μmol L−1, respectively. Human saliva samples were collected from healthy individuals and patients previously diagnosed with periodontitis or diabetes and then analyzed on the proposed μPADs. The results found using μPADs revealed higher glucose concentration values in saliva collected from patients diagnosed with diabetes mellitus and greater nitrite concentrations in saliva collected from patients diagnosed with periodontitis, as expected. The results obtained on μPADs did not differ statistically from those measured by spectrophotometry. With the aim of developing paper-based wearable sensors, μPADs were integrated, for the first time, into a silicone mouthguard using a 3D-printed holder. The proof of concept was successfully demonstrated through the monitoring of the glucose concentration in saliva after the ingestion of chocolate. According to the results reported herein, paper-based microfluidic devices offer great potential for salivary diagnostics, making their integration into a silicone mouthguard possible, generating simple, low-cost, instrument-free, and powerful wearable sensors.

Salivary diagnostics on paper microfluidic devices and their use as wearable sensors for glucose monitoring

Novel approaches for colorimetric measurements in analytical chemistry - A review

This study presents a simple, fast, and sensitive method for multiplexing heavy metal detection. Using a chemically patterned microfluidic paper-based analytical device (C-μPAD), silane compounds terminating in amine (NH2), carboxyl (COOH), and thiol (SH) were immobilized on a patterned chromatography paper via condensation reactions. Three chromogenic reagents that react distinctly with Ni(II), Cr(VI), and Hg(II) were then covalently coupled to these functional groups. These functionalized C-μPADs were then evaluated for heavy metals ions detection with spiked water samples. Using a single-plex platform, we achieved detection limits as low as 0.24 ppm for Ni(II), 0.18 ppm for Cr(VI) and 0.19 ppm for Hg(II). The detection limits for this single-plex platform were twice as good as those obtained in previous studies using colorimetric analysis due to the formation of homogeneous metal complexes from immobilized chromogenic reagents. Furthermore, by minimizing cross-reaction with chelating agents and maximizing reaction uniformity, multiplex heavy metal ion detection was successfully demonstrated for lake-water samples spiked with various concentrations of heavy metal ions with high precision. This functionalized C-μPAD provides a highly portable and rapid on-site monitoring platform for multiple heavy metal ions detection with extremely high repeatability, which is useful for resource-limited areas and developing countries.

Eduardo Luiz Rossini

Papers

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

Authentication of roasted and ground coffee samples containing multiple adulterants using NMR and a chemometric approach

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

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

Bioactive paper platform for detection of hydrogen peroxide in milk