Alcohol-Triggered Capillarity through Porous Pyrolyzed Paper-Based Electrodes Enables Ultrasensitive Electrochemical Detection of Phosphate

Abstract

The sensing field has shed light on an urgent necessity for field-deployable, user-friendly, sensitive, and scalable platforms that are able to translate solutions into the real world. Here, we attempt to meet these requests by addressing a simple, low-cost, and fast electrochemical approach to provide sensitive assays that consist of dropping a small volume (0.5 μL) of off-the-shelf alcohols on pyrolyzed paper-based electrodes before adding the sample (150 μL). This method was applied in the detection of phosphate after the formation of the phosphomolybdate complex (250–860 nm in size). Prior drops of isopropanol allow for the fast penetration of the sample through pores of this hydrophobic paper, delivering hindrance-free redox reactions across increasing active areas and ultimately improving the detection performance. The sensitivity (−1.9 10–6 mA cm–2 ppb–1) and limit of detection (1.1 ppb) were improved, respectively, by factors of 33 and 99 over the data achieved without the addition of isopropanol, listing among the lowest values when compared with those results reported in the literature for phosphate (expressed in terms of the concentration of phosphorus). The approach enabled the quantification of this analyte in real samples with accuracies ranging from 87 to 103%. Furthermore, preliminary measurements demonstrated the successful performance of the electrodes with prior addition of other widely used alcohols, that is, methanol and ethanol. These results may extend the applicability of the method. In special, the scalability and eco-friendly character of the electrode fabrication combined with the sensitivity and simplicity of the analyses make the developed platform a promising alternative that may help to pave the way for a new generation of disposable sensors toward the daily monitoring of phosphate in water samples, thus contributing to prevent ecological side effects.

Paper-based sensors for diagnostics, human activity monitoring, food safety and environmental detection

“…By means of functional nanomaterials modified on this electrode, the detection of SARS-CoV-2 was achieved. Shimizu et al 94 achieved sensitive detection of phosphate using pyrolytic paper modified with isopropyl alcohol as a porous electrode. This pyrolytic paper can be produced in large quantities and can create independent structures in one cutting operation using a commercial knife plotter, demonstrating that pyrolytic paper is a promising alternative to standard electrodes.…”

Biocompatible Wearable Electrodes on Leaves toward the On-Site Monitoring of Water Loss from Plants

“…Further, the paper is a low-cost, broadly available, and biodegradable material. 15,17 Scalable electrodes consisting of Ni patterns attained by wellestablished microfabrication approaches and ecofriendly pyrolyzed paper enabled reproducible and sensitive tests. Both sensors operated through the direct transfer of conductive materials on hairy soy leaves using an ordinary adhesive tape.…”

“…Stand-alone Ni structures (SANSs) were fabricated by photolithographic and electroplating steps, whereas pyrolyzed graphitic paper (PGP) was attained by pyrolysis on a furnace (Figure S1). ,, The SANS comprised two pads (5.0 mm × 8.0 mm) for electrical contact with a potentiostat and concentric semicircles (1.5 mm width; sensing area) interconnected by serpentine traces (500.0 μm width; Video S1). PGP-based interdigitated electrodes (2.0 mm width and 1.0 mm gap) were fabricated via a knife plotter (Video S2).…”

“…We used two types of electrodes with complementary merits, i.e., stand-alone thick films of Ni patterned by well-established microfabrication techniques and an ecofriendly option that was based on graphitic paper attained by pyrolysis on a furnace. The latter offers a scalable way to achieve carbon electrodes without the use of liquid chemicals or waste generation. − nano-XRF analyses provided by a nanobeam allowed us to probe the sensor-exposed leaf regions to assess the long-term compatibility of Ni electrodes at the nanoscale, which was revealed to not disturb the natural processes of leaves. Soy was selected as our study model because of its relevance for Brazil’s trade balance and because it is a fast-growing plant with high water loss levels, hence showing a critical dependence on drought stress and other damaging phenomena. , …”

An amphiprotic paper-based electrode for glucose detection based on layered carbon nanotubes with silver and polystyrene particles

“…These properties make paper promising for colorimetric, 16 uorescence, 17 chemiluminescence, 18 absorbance, 19 Raman spectroscopy, 20 mass spectrometry, 21 and electrochemical detection. 22 Currently, electrochemical detection has been combined with paper-based platforms following the strategies of printing, [23][24][25][26] evaporation and sputtering, 27,28 electrodeposition, 29 pencil-drawing, 30,31 drop-casting deposition, 32,33 pyrolysis, 22,34 and vacuum-ltration. [35][36][37] In contrast to other strategies, vacuum ltration is a relatively simple, time-saving, and scalable method for fabricating paper electrodes in electrochemical detection.…”