Flexible Laser-Induced Graphene for Nitrogen Sensing in Soil

Abstract

Flexible graphene electronics are rapidly gaining interest, but their widespread implementation has been impeded by challenges with ink preparation, ink printing, and post-print annealing processes. Laser-induced graphene (LIG) promises a facile alternative by creating flexible graphene electronics on polyimide substrates through a one-step laser writing fabrication method. Herein we demonstrate the use of LIG, created through a low-cost UV laser, for electrochemical ion selective sensing of plant-available nitrogen (i.e., both ammonium and nitrate ions: NH4+ and NO3-) in soil samples. The laser used to create the LIG was operated at distinct pulse rates (10, 20, 30, 40, and 50 ms) in order to maximize the LIG electrochemical reactivity. Results illustrated that a laser pulse rate of 20 ms led to a high percentage of sp2 carbon (77%) and optimal peak oxidation current of 120 uA during ferricyanide cyclic voltammetry. Therefore, LIG electrodes created with a 20 ms pulse rate were consequently functionalized with distinct ionophores specific to NH4+(nonactin) or NO3-(tridodecylmethylammonium nitrate) within polyvinyl chloride (PVC)-based membranes to create distinct solid contact ion selective electrodes (SC-ISEs) for NH4+ and NO3-ion sensing respectively. The LIG SC-ISEs displayed near Nernstian sensitivities of 51.7 ± 7.8 mV/decade (NH4+) and -54.8 ± 2.5 mV/ decade (NO3-), detection limits of 28.2 ± 25.0 uM (NH4+) and 20.6 ± 14.8 uM (NO3-), low long-term drift of 0.93 mV/hr (NH4+) sensors and -5.3 μV/hr (NO3-) sensors and linear sensing ranges within 10-5-10-1 M for both sensors. Moreover, soil slurry sensing was performed and recovery percentages of 96% and 95% were obtained for added NH4+and NO3-, respectively. These results, combined with a facile fabrication that does not require metallic nanoparticle decoration, make these LIG electrochemical sensors appealing for a wide range of in field or point-of-service applications for soil health management. ABSTRACTFlexible graphene electronics are rapidly gaining interest, but their widespread implementation has been impeded by challenges with ink preparation, ink printing, and postprint annealing processes. Laser-induced graphene (LIG) promises a facile alternative by creating flexible graphene electronics on polyimide substrates through a one-step laser writing fabrication method. Herein we demonstrate the use of LIG, created through a low-cost UV laser, for electrochemical ion selective sensing of plant-available nitrogen (i.e., both ammonium and nitrate ions: NH 4 + and NO 3 -metallic nanoparticle decoration, make these LIG electrochemical sensors appealing for a wide range of in-field or point-of-service applications for soil health management.

UV Laser‐Induced Polyimide‐to‐Graphene Conversion: Modeling, Fabrication, and Application

“…However, the underlying conversion mechanism for this method is still unclear, and the key parameters to ensure high‐quality graphene are yet to be identified. A molecular dynamics (MD) simulation study by Dong et al suggests that under extreme conditions of high pressure (≈3 GPa) and temperature (>2400 K), which mimic those generated by the infrared laser induction, it is possible to form crystallized layered graphene clusters from PI without the assistance of metal catalysts; this result is consistent with previous experimental observations; on the other hand, recent work show that if UV laser, instead of infrared laser, is used in the conversion process, only very poor quality graphene can be produced, due possibly to the poor absorption of UV light by the carbon source or unoptimized processing conditions.…”

“…[26] However, the underlying conversion mechanism for this method is still unclear, and the key parameters to ensure high-quality graphene are yet to be identified. A molecular dynamics (MD) simulation study by Dong et al suggests that under extreme conditions of high pressure (≈3 GPa) and temperature (>2400 K), which mimic those generated by the infrared laser induction, it is possible to form crystallized layered graphene clusters from PI without the assistance of metal catalysts; this result is consistent with previous experimental observations; [39] on the other hand, recent work [40,41] show that if UV laser, instead of infrared laser, is used in the conversion process, only very poor quality graphene can be produced, due possibly to the poor absorption of UV light by the carbon source or unoptimized processing conditions.In this study, we investigated in-depth the light-material interaction by developing a reactive MD model to disclose the transient process that leads to LIG formation and identified the critical parameters that govern this process. Following the theoretical prediction, we have experimentally demonstrated that picosecond UV laser processing can also be used to prepare high-quality LIG from PI at ambient conditions.…”

Ion‐Selective Sensors Based on Laser‐Induced Graphene for Evaluating Human Hydration Levels Using Urine Samples

“…Such ISEs have therefore been implemented in a wide variety of applications including in situ water quality analysis, [ 3 ] electrolyte sensing in sweat, [ 4 ] and fertilizer monitoring in soils. [ 5 ] However, solid‐state ISEs are often prone to large signal drift, which may be caused by the formation of an aqueous layer between the ion‐selective membrane and the electrode. These sensors often require expensive materials such as noble metals or metallic nanoparticles to provide sufficient electrode conductivity and surface area for sensitive ion sensing.…”

“…Graphene‐based electrodes hold tremendous promise for electrochemical biosensing including ion selective sensing [ 4c,5,6 ] due to their exceptional material properties, such as high electrical conductivity, strength, and ability to be functionalized with chemical moieties that are suitable for binding with a wide variety of biorecognition agents. [ 7 ] A variety of carbon‐based nanomaterials (i.e., fullerenes, carbon‐nanotubes, and graphene) have all been incorporated into solid‐state ISEs to increase electroactive surface of the electrode; ion‐selective membrane to electrode adhesion; and consequently, to improve signal sensitivity and stability while minimizing drift.…”

Solid Contact Nitrate Ion‐selective Electrode Based on Cobalt(II) Complex with 4,7‐Diphenyl‐1,10‐phenanthroline

“…The advantage of the tested electrode is its very simple construction without an additional intermediate layer. [36] graphite powder Ppy(NO 3 À ) 5.4 × 10 À 5 1.5 × 10 À 4 -1.0 × 10 À 1 À 57.1 4.3-7.4 ClO 4 À , SCN À , Br À , I À , CN À [40] graphite TDMAN 3.0 × 10 À 5 5.0 × 10 À 5 -1.0 × 10 À 1 À 57.9 nr Cl À (ClO 4 À , SCN À Br À -nr) [37] MWCNTs TDMAN 2.5 × 10 À 6 3.2 × 10 À 6 -1.0 × 10 À 1 À 57.7 ClO 4 À , SCN À , NO 2 À , Cl À [39] TTFÀ TCNQ Nitrate ionophoreV 3.2 × 10 À 6 1.0 × 10 À 5 -1.0 × 10 À 1 À 58.5 nr NO 2 À (ClO 4 À , SCN À Br À -nr) [41] Laser induced graphene TDMAN 2.1 × 10 À 5 5.0 × 10 À 5 -1.0 × 10 À 1 À 54.8 nr nr [42] POTÀ MoS 2 nanocomposite TDMAN 9.2 × 10 À 5 7.1 × 10 À 4 -1.0 × 10 À 1 À 64.0 nr nr [35,43] DX262 NO 3 -ISE 3.0 × 10 À 5 3.0 × 10 À 5 -1.0 À 57.0 2-12 ClO 4 À , SCN À , Br À , I À , CN À , BF 4 À , salicylate this work Ag/AgCl/Cl À Co(Bphen) 2 (NO 3 ) 2 3.98 × 10 À 6 1.0 × 10 À 5 -1.0 × 10 À 1 À 56.3 5.4-10.6 ClO 4 À , SCN À , Br À TTFÀ TCNQ -tetrathiafulvaleneÀ tetracyanoquinodimethane; MWCNTs -miltiwalled carbon nanotubes; Ppy(NO 3 À ) -polypyrolle doped with nitrate; TDMAN -tridodecylmethylaminium nitrate; DX262 NO 3 -ISE -conventionalnitrate ISE offered by METTLER TOLEDO nr -not reported.…”