Rapid determination of salicylic acid at screen printed electrodes

Advancing abiotic stress monitoring in plants with a wearable non-destructive real-time salicylic acid laser-induced-graphene sensor

Drought and salinity stresses present significant challenges that exert a severe impact on crop productivity worldwide. Understanding the dynamics of salicylic acid (SA), a vital phytohormone involved in stress response, can provide valuable insights into the mechanisms of plant adaptation to cope with these challenging conditions. This paper describes and tests a sensor system that enables real-time and non-invasive monitoring of SA content in avocado plants exposed to drought and salinity. By using a reverse iontophoretic system in conjunction with a laser-induced graphene electrode, we demonstrated a sensor with high sensitivity (82.3 nA/[μmol L-1⋅cm-2]), low limit of detection (LOD, 8.2 μmol L-1), and fast sampling response (20 s). Significant differences were observed between the dynamics of SA accumulation in response to drought versus those of salt stress. SA response under drought stress conditions proved to be faster and more intense than under salt stress conditions. These different patterns shed light on the specific adaptive strategies that avocado plants employ to cope with different types of environmental stressors. A notable advantage of the proposed technology is the minimal interference with other plant metabolites, which allows for precise SA detection independent of any interfering factors. In addition, the system features a short extraction time that enables an efficient and rapid analysis of SA content.

A novel ratiometric fluorescent probe based on dual-emission carbon dots for highly sensitive detection of salicylic acid

In this study, a novel ratiometric fluorescence probe based on dual-emission carbon dots (CDs) for the sensitive detection of salicylic acid (SA) was constructed for the first time. The dual-emission CDs were synthesized by simple hydrothermal method using tartaric acid (TA) and m-phenylenediamine (mPD) as raw materials. In the presence of SA, the fluorescence intensity of CDs was enhanced at 499 nm, but remained basically unchanged at 439 nm. This phenomenon is caused by the intermolecular hydrogen bond interactions. The concentrations of SA had an excellent linear relationship with CDs' fluorescence intensity ratio (F499/F439) in a range of 1 ∼ 120 and 120 ∼ 240 μM with low detection limits of 0.68 and 1.05 μM. The established ratiometric fluorescent probe is economical, simple and green, and can be used for the effective detection of SA. In addition, the proposed ratiometric fluorescent probe was successfully used to monitor SA in facial mask and toning lotion samples with a satisfactory recovery of 99.7-106.7 %. The results show that the constructed fluorescent probe based on dual-emission CDs has a great potential for the rapid and sensitive analysis of SA in actual samples.

All-solid-state potentiometric salicylic acid sensor for in-situ measurement of plant

Using PEDOT as the conductive polymer, an innovative small-scale sensor for directly measuring salicylate ions in plants was developed, which avoided the complicated sample pretreatment of traditional analytical methods and realized the rapid detection of salicylic acid. The results demonstrate that this all-solid-state potentiometric salicylic acid sensor is easy to miniaturize, has a longer lifetime (≥1 month), is more robust, and can be directly used for the detection of salicylate ions in real samples without any additional pretreatment. The developed sensor has a good Nernst slope (63.6 ± 0.7 mV/decade), the linear range is 10^-2 ~ 10^-6 M, and the detection limit can reach (2.8 × 10^-7 M). The selectivity, reproducibility, and stability of the sensor were evaluated. The sensor can perform stable, sensitive, and accurate in situ measurement of salicylic acid in plants, and it is an excellent tool for determining salicylic acid ions in plants in vivo.

A novel multi-set differential pulse voltammetry technique for improving precision in electrochemical sensing

Over the years, electrochemical sensors have achieved high levels of sensitivity due to advancements in electrical circuits and systems, and calibration standards. However, little has been explored towards developing ways to minimize random errors and improve the precision of electrochemical sensors. In this work, a novel electrochemical method derived from differential pulse voltammetry termed multi-set differential pulse voltammetry (MS-DPV) is proposed with the goal of reducing random errors in chemical- and bio-sensors and thereby improve precision. The proposed MS-DPV improves precision without the need to replicate measurements. Therefore, saving energy use, time consumed, and/or materials required. The method is especially suited for portable or in-field sensing solutions that have strict constraints on sampling, time and energy use. To realize the proposed method, a custom designed plug-and-play-type electrochemical sensing system was employed which was then used for detecting salicylic acid (SA). SA is a key phytohormone deployed during defense responses in plants against biotic stresses. Additionally, SA is widely used in the pharmaceutical and healthcare industry due to its anti-inflammatory and analgesic properties. Using a "4-set-DPV", an error reduction of up to 12% was observed in SA detection when compared to conventional differential pulse voltammetry. In general, the error variance reduces linearly with the number of readings taken in a single scan of the proposed MS-DPV.

Determination of Salicylic Acid Using a Highly Sensitive and New Electroanalytical Sensor

Background:

A drug sensor (salicylic acid, in this case) was designed and made up of this research. The senor was made by modification of paste electrode (MPE) with CuO-SWCNTs and 1-hexyl-3-methylimidazolium chloride (HMICl). The MPE/CuO-SWCNTs/HMICl showed catalytic activity for the oxidation signal of salicylic acid in phosphate buffer solution.

Methods:

Electrochemical methods were used as a powerful strategy for the determination of salicylic acid in pharmaceutical samples. Aiming at this goal, carbon paste electrode was amplified with conductive materials and used as a working electrode.

Results:

The MPE/CuO-SWCNTs/HMICl was used for the determination of salicylic acid in the concentration range of 1.0 nM – 230 µM using differential pulse voltammetric (DPV) method. At pH=7.0, as optimum condition, the MPE/CuOSWCNTs/HMICl displayed a high-quality ability for the determination of salicylic acid in urine, pharmaceutical serum, and water samples.

Conclusion:

The MPE/CuO-SWCNTs/HMICl was successfully used as a new and high performance working electrode for the determination of salicylic acid at a nanomolar level and in real samples.

Sensing Methodologies in Agriculture for Monitoring Biotic Stress in Plants Due to Pathogens and Pests

Reducing agricultural losses is an effective way to sustainably increase agricultural output efficiency to meet our present and future needs for food, fiber, fodder, and fuel. Our ever-improving understanding of the ways in which plants respond to stress, biotic and abiotic, has led to the development of innovative sensing technologies for detecting crop stresses/stressors and deploying efficient measures. This article aims to present the current state of the methodologies applied in the field of agriculture towards the detection of biotic stress in crops. Key sensing methodologies for plant pathogen (or phytopathogen), as well as herbivorous insects/pests are presented, where the working principles are described, and key recent works discussed. The detection methods overviewed for phytopathogen-related stress identification include nucleic acid-based methods, immunological methods, imaging-based techniques, spectroscopic methods, phytohormone biosensing methods, monitoring methods for plant volatiles, and active remote sensing technologies. Whereas the pest-related sensing techniques include machine-vision-based methods, pest acoustic-emission sensors, and volatile organic compound-based stress monitoring methods. Additionally, Comparisons have been made between different sensing techniques as well as recently reported works, where the strengths and limitations are identified. Finally, the prospective future directions for monitoring biotic stress in crops are discussed.

Ratiometric electrochemical sensor for accurate detection of salicylic acid in leaves of living plants

Detection of signal molecules in living plants is of great relevance for precision farming. In this work, to establish a more effective method for monitoring salicylic acid (SA) in the leaves of living plants, a ratiometric electrochemical sensor was fabricated based on a Cu metal-organic framework (Cu-MOF) and carbon black (CB) composite. The Cu-MOF and CB composite was used to catalyze SA oxidation. Ratiometric oxidation current peak intensities I SA/I Cu-MOFs were used as the response signal for SA. I SA/I Cu-MOFs linearly enhanced with the increase of SA concentration, together with low limits of detection (12.50 μM). Moreover, our sensor is fabricated on a screen-printed electrode (SPE), which is especially suitable for applying to the flat leaves of plants. Using this sensor, the SA level in the leaves of cucumber seedlings was monitored in vivo under salt stress. The proposed sensor is accurate, reliable and practical. This is the first report for developing a ratiometric electrochemical sensor for detecting SA in living plants. Our work can also provide a strategy for in vivo studies on the leaves of plants.

Electro-Oxidation and Simultaneous Determination of Indole-3-Acetic Acid and Salicylic Acid on Graphene Hydrogel Modified Electrode

A selective and sensitive electrochemical sensor was developed for simultaneous detection of phytohormones indole-3-acetic acid (IAA) and salicylic acid (SA). The sensing interface was fabricated on a porous, three-dimensional networked graphene hydrogel (GH) modified glassy carbon electrode (GCE). The electrocatalytic behavior of IAA and SA on the surface of the modified electrode (GH/GCE) was investigated by cyclic voltammetry and linear sweep voltammetry. Results show that the oxidation reactions of IAA and SA occur at different potentials, which enable their simultaneous detection at the sensing interface. Under optimal conditions, the GH/GCE exhibited good selectivity and stability and its response, unaffected by various interferents, was linear in the range of 4 to 200 μM of IAA and SA. The limit of detection (S/N = 3) achieved were 1.42 μM for IAA and 2.80 μM for SA. The sensor performance was validated by measuring for IAA and SA in real vegetable samples with satisfactory results.

Gold nanoparticle-doped three-dimensional reduced graphene hydrogel modified electrodes for amperometric determination of indole-3-acetic acid and salicylic acid

Three-dimensional (3D) networked nanomaterials have attracted great interest because of their unique porous and 3D-networked structures. In this work, a series of gold nanoparticle (AuNP) doped graphene hydrogel nanocomposites (AuNP-GHs) were synthesized through hydrothermal reaction under various conditions. X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS) were used to characterize the AuNP-GH. The AuNP-GH was used to modify the glassy carbon electrode (GCE) for the detection of indole-3-acetic acid (IAA) and salicylic acid (SA) using chronoamperometric measurements. Under optimum conditions, the AuNP-GH/GCE exhibited linear response to IAA in the ranges of 0.8-4 μM and 4-128 μM, and to SA in the ranges of 0.8-8.4 μM and 8.4-188.4 μM. The detection limits (S/N = 3) were calculated to be 0.21 μM for IAA and 0.22 μM for SA. The proposed sensor showed good sensitivity and stability and hence it was applied in the detection of IAA and SA in spiked samples with satisfactory results.

A Review: New Trends in Electrode Systems for Sensitive Drug and Biomolecule Analysis

Drug and biomolecule analysis with high precision, fast response, not expensive, and user-friendly methods have been very important for developing technology and clinical applications. Electrochemical methods are highly capable for assaying the concentration of electroactive drug or biomolecule and supply excellent knowledge concerning its physical and chemical properties such as electron transfer rates, diffusion coefficients, electron transfer number, and oxidation potential. Electrochemical methods have been widely applied because of their accuracy, sensitivity, cheapness, and can applied on-site determinations of various substances. The progress on electronics has allowed developing reliable, more sensitive and less expensive instrumentations, which have significant contribution in the area of drug development, drug and biomolecule analysis. The developing new sensors for electrochemical analysis of these compounds have growing interest in recent years. Screen-printed based electrodes have a great interest in electrochemical analysis of various drugs and biomolecules due to their easy manufacturing procedure of the electrode allow the transfer of electrochemical laboratory experiments for disposable on-site analysis of some compounds. Paper based electrodes are also fabricated by new technology. They can be preferred due to their easy, cheap, portable, disposable, and offering high sensitivity properties for many application field such as environmental monitoring, food quality control, clinical diagnosis, drug, and biomolecules analysis. In this review, the recent electrochemical drug and biomolecule (DNA, RNA, µRNA, Biomarkers, etc.) studies will be presented that involve new trend disposable electrodes.

A carbon paste electrode modified with a nickel titanate nanoceramic for simultaneous voltammetric determination of ortho- and para-hydroxybenzoic acids

An electrochemical sensor is described for the simultaneous determination of ortho-hydroxybenzoic acid (OHB) and para-hydroxybenzoic acid (PHB). The sensor consists of a carbon paste electrode modified with nickel titanate nanoceramics (NiTiO₃/CPE). The NiTiO₃ nanoceramics and the nanostructured modified CPE were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, electrochemical impedance spectroscopy and cyclic voltammetry. Differential pulse voltammetry indicates that the response to OHB (best measured at 0.90 V vs. Ag/AgCl) and PHB (measured at 0.80 V vs. Ag/AgCl) is significantly improved at the modified CPE compared to a bare CPE. The limits of detection (at S/N = 3) are 0.38 and 0.10 μM for OHB and PHB, respectively. The method was applied to the determination of the two isomers in peeling skin lotion and during the Kolbe-Schmitt reaction. Graphical abstract Nickel titanate nanoceramics (NiTiO₃) were synthesized by a sol-gel method. Then, a carbon paste electrode modified with NiTiO₃ (NiTiO₃/CPE) was constructed. The modified electrode was applied to the interference-free and simultaneous determination of ortho-hydroxybenzoic acid (OHB) and para-hydroxybenzoic acid (PHB).

Reusability of SPE and Sb-modified SPE Sensors for Trace Pb(II) Determination

In this work, unmodified screen-printed electrode (bare SPE) and Sb-film modified SPE (SbFSPE) sensors were employed for the analysis of trace amounts of Pb(II) in non-deaerated water solutions. The modified electrode was performed in situ in 0.5 mg/L Sb(III) and 0.01 M HCl. The methodology was validated for an accumulation potential of ⁻1.1 V vs. Ag/AgCl and an accumulation time of 60 s. A comparative analysis of bare SPE and SbFSPE showed that the detection and quantification limits decrease for the bare SPE. The method with the bare SPE showed a linear response in the 69.8⁻368.4 µg/L concentration range, whereas linearity for the SbFSPE was in the 24.0⁻319.1 µg/L concentration range. This work also reports the reason why the multiple standard addition method instead of a linear calibration curve for Pb(II) analysis should be employed. Furthermore, the analytical method employing SbFSPE was found to be more accurate and precise compared to the use of bare SPE when sensors were employed for the first time, however this performance changed significantly when these sensors were reused in the same manner. Furthermore, electrochemical impedance spectroscopy was used for the first time to analyse the electrochemical response of sensors after being used for multiple successive analyses. Surface characterisation before and after multiple successive uses of bare SPE and SbFSPE sensors, with atomic force microscopy and field emission scanning electron microscopy, showed sensor degradation. The interference effect of Cd(II), Zn(II), As(III), Fe(II), Na(I), K(I), Ca(II), Mg(II), NO₃⁻, Bi(III), Cu(II), Sn(II), and Hg(II) on the Pb(II) stripping signal was also studied. Finally, the application of SbFSPE was tested on a real water sample (from a local river), which showed high precision (RSD = 8.1%, n = 5) and accurate results.