In situ grown TiO2 nanorod arrays functionalized by molecularly imprinted polymers for salicylic acid recognition and detection

Electrochemical needle sensor based on a B, N co-doped graphene microelectrode array for the on-site detection of salicylic acid in fruits and vegetables

In this study, a microelectrode array sensor based on boron and nitrogen co-doped vertical graphene (BNVG) was assembled to quantify salicylic acid (SA) in living plants. The influence of B and N contents on the electrochemical reaction kinetics and SA response signal was investigated. A microneedle sensor with three optimized BNVG microelectrodes (3.57 at.% B and 3.27 at.% N) was used to quantitatively analyze SA in the 0.5-100 μM concentration range and pH 4.0-9.0, with limits of detection of 0.14-0.18 μM. Additionally, a quantitative electrochemical model database based on the BNVG microelectrode sensor was constructed to monitor the growth of cucumbers and cauliflowers, which confirmed that the SA level and plant growth rate were positively correlated. Moreover, the SA levels in various vegetables and fruits purchased from the market were measured to demonstrate the practical application prospects for on-site inspection and evaluation.

MOFs@POMs-derived bimetallic oxide Fe2(MoO4)3 nanoparticles for sensitive colorimetric detection of salicylic acid in aspirin

A colorimetric sensing method for salicylic acid (SA) was developed by designing and fabricating bimetallic oxide nanozymes. Firstly, by calcinating MIL-100(Fe)@PMo12 (MOFs@POMs) at different temperature, Fe2(MoO4)3-Ts (T = 400℃, 500℃, 600℃, 700℃) nanoparticles (NPs) were successfully prepared. Secondly, by evaluating the peroxidase-like activities, Fe2(MoO4)3-600 NPs shows the best peroxidase-like activity attributed to the Fenton-like effect and the synergistic coupling interaction between Mo and Fe. Finally, based on the specific complexation between SA and Fe3+, a sensitive colorimetric sensor for SA was established, which exhibits superior selectivity and interference with a detection limit of 0.11 μM and a linear range of 10 to 100 μM, the lowest LOD for SA to date, to the best of our knowledge.

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.

A hybrid multifunctional physicochemical sensor suite for continuous monitoring of crop health

This work reports a first-of-its-kind hybrid wearable physicochemical sensor suite that we call PlantFit for simultaneous measurement of two key phytohormones, salicylic acid, and ethylene, along with vapor pressure deficit and radial growth of stem in live plants. The sensors are developed using a low-cost and roll-to-roll screen printing technology. A single integrated flexible patch that contains temperature, humidity, salicylic acid, and ethylene sensors, is installed on the leaves of live plants. The strain sensor with in-built pressure correction capability is wrapped around the plant stem to provide pressure-compensated stem diameter measurements. The sensors provide real-time information on plant health under different amounts of water stress conditions. The sensor suite is installed on bell pepper plants for 40 days and measurements of salicylic acid, ethylene, temperature, humidity, and stem diameter are recorded daily. In addition, sensors are installed on different parts of the same plant to investigate the spatiotemporal dynamics of water transport and phytohormone responses. Subsequent correlation and principal component analyses demonstrate the strong association between hormone levels, vapor pressure deficit, and water transport in the plant. Our findings suggest that the mass deployment of PlantFit in agricultural settings will aid growers in detecting water stress/deficiency early and in implementing early intervention measures to reduce stress-induced yield decline.

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.

High-sensitivity photo-electrochemical heterostructure of the cuprous oxide-metal organic framework for a dioctyl phthalate molecularly imprinted sensor

This work designed a novel dioctyl phthalate (DOP) photoelectrochemical (PEC) sensor based on a molecularly imprinted polymer (MIP) modified Cu₃(BTC)₂@Cu₂O heterostructure. In this work, a metal organic framework (MOF), Cu₃(BTC)₂, was coated on Cu₂O through a simple immersion method to form a Cu₃(BTC)₂@Cu₂O heterostructure. The heterostructure exhibited strong light adsorption ability, good stability and enhanced photocurrent under visible light irradiation. Using the Cu₃(BTC)₂@Cu₂O heterostructure as the photoelectric converter, a PEC sensor was constructed by imprinting DOP on the heterostructure. Under the optimal experimental conditions, the PEC sensor showed a wide linear range from 25.0 pM-0.1 μM and a low detection limit of 9.15 pM. This method with good sensitivity, stability, selectivity and reproducibility in actual sample analyses showed promising applications of the MOF-based heterostructure in photoelectrochemical analysis fields.