In this work, we demonstrate the first example of fully printed carbon nanomaterials on paper with unique features, aiming the fabrication of functional electronic and electrochemical devices. Bare and modified inks were prepared by combining carbon black and cellulose acetate to achieve high-performance conductive tracks with low sheet resistance. The carbon black tracks withstand extremely high folding cycles (>20 000 cycles), a new record-high with a response loss of less than 10%. The conductive tracks can also be used as 3D paper-based electrochemical cells with high heterogeneous rate constants, a feature that opens a myriad of electrochemical applications. As a relevant demonstrator, the conductive ink modified with Prussian-blue was electrochemically characterized proving to be very promising toward the detection of hydrogen peroxide at very low potentials. Moreover, carbon black circuits can be fully crumpled with negligible change in their electrical response. Fully printed motion and wearable sensors are additional examples where bioinspired microcracks are created on the conductive track. The wearable devices are capable of efficiently monitoring extremely low bending angles including human motions, fingers, and forearm. Here, to the best of our knowledge, the mechanical, electronic, and electrochemical performance of the proposed devices surpasses the most recent advances in paper-based devices.
A simple and fast fabrication method to create high-performance pencil-drawn electrochemical sensors is reported for the first time. The sluggish electron transfer observed on bare pencil-drawn surfaces was enhanced using two electrochemical steps: first oxidizing the surface and then reducing it in a subsequent step. The heterogeneous rate constant was found to be 5.1 × 10 cm s, which is the highest value reported so far for pencil-drawn surfaces. We mapped the origin of such performance by atomic force microscopy, X-ray photoelectron spectroscopy, and Raman spectroscopy. Our results suggest that the oxidation process leads to chemical and structural transformations on the electrode surface. As a proof-of-concept, we modified the pencil-drawn surface with Meldola's blue to electrocatalytically detect nicotinamide adenine dinucleotide (NADH). The electrochemical device exhibited the highest catalytic constant (1.7 × 10 L mol s) and the lowest detection potential for NADH reported so far in paper-based electrodes.
This work presents a simple, low cost method for creating microelectrodes for electrochemical paper-based analytical devices (ePADs). The microelectrodes were constructed by backfilling small holes made in polyester sheets using a CO2 laser etching system. To make electrical connections, the working electrodes were combined with silver screen-printed paper in a sandwich type two-electrode configuration. The devices were characterized using linear sweep voltammetry and the results are in good agreement with theoretical predictions for electrode size and shape. As a proof-of-concept, cysteine was measured using cobalt phthalocyanine as a redox mediator. The rate constant (kobs) for the chemical reaction between cysteine and the redox mediator was obtained by chronoamperometry and found to be on the order of 105 s−1 M−1. Using a microelectrode array, it was possible to reach a limit of detection of 4.8 μM for cysteine. The results show that carbon paste microelectrodes can be easily integrated with paper-based analytical devices.
Paper has become increasingly recognized as a very interesting substrate for the construction of microfluidic devices, with potential application in a variety of areas, including health diagnosis, environmental monitoring, immunoassays and food safety. The aim of this review is to present a short history of analytical systems constructed from paper, summarize the main advantages and disadvantages of fabrication techniques, exploit alternative methods of detection such as colorimetric, electrochemical, photoelectrochemical, chemiluminescence and electrochemiluminescence, as well as to take a closer look at the novel achievements in the field of bioanalysis published during the last 2 years. Finally, the future trends for production of such devices are discussed.
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.
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