Paper-based Sensor Research Articles

Preparation of Paper-Based Fluorescent Sensors and Their Application for the Detection of Cu2+ in Water.

Excessive copper (Cu2+) causes adverse effects on human health and the ecological environment. Traditional methods for detecting Cu2+ have drawbacks such as high detection costs, complex operating conditions, and being time consuming. Therefore, there is an urgent need to develop simple detection methods to better meet specific health and environment quality needs. In this work, a paper-based fluorescence sensor was prepared (herein referred to as the as-prepared method) by immersing filter paper in aqueous polyethyleneimine (PEI) solution, and its potential use in Cu2+ detection was investigated. The results showed that the as-prepared paper samples, with fluorescence properties obtained by aggregation-induced luminescence of PEI, have selective recognition of Cu2+ based on the internal filtration effect, and the lowest detection limit is 0.03 μM. In addition, the relative error of this method is in the range of 1.80~2.23%, which is relatively comparable to the national standard method (0.63~630 μM), demonstrating high accuracy. Therefore, paper-based sensors with a simple preparation method have potential applications in the detection of Cu2+ in water.

Detection of volatile primary aliphatic amines: Highly selective and sensitive vapoluminescent sensing of n-butylamine

Detection of volatile amines is of great interest for environmental and industrial monitoring for the protection of human health from exposure to toxic substances. This contribution describes the vapochromic and vapoluminescent properties of a Lewis acidic Zn(salen)-type Schiff-base complex and its application as a chemosensor for detection of n-butylamine (BA) vapors. Annealed films of the complex were initially involved for vapochromic and vapoluminescence screening experiments to evaluate their response towards compounds representative of each of the different chemical classes of volatile organic compounds (VOCs). Then, a cost-effective, disposable paper-based vapoluminescent sensor, characterized by high optical uniformity and repeatability, was developed for the selective and sensitive direct in-situ detection of BA vapors. Under static exposure conditions, the sensor allows a sensitive vapoluminescent detection of BA, with a LOD down to 2.0 ppm, below the permissible exposure limit of 5 ppm established by OSHA for BA, and a linear dynamic range up to 50 ppm. The sensor response is not affected by the exposure temperature, only a different exposure time is required as the temperature varies, while average relative humidity levels lead to almost negligible changes in the sensor response. The sensor is highly selective for BA with respect to ammonia and the different chemical classes of VOCs, including relevant primary aliphatic amines, with the exception of propylamine and sec-butylamine, especially at low concentrations (tens of ppm). Selectivity for BA is also demonstrated by competitive experiments in the presence of a 10-fold ppm amount of all representative VOCs of each class as potential interferents.

A flexible paper based strain sensors drawn by pencil for low-cost pressure sensing applications

Paper-based strain sensors, offering a cost-effective and environmentally friendly solution, are in demand for pressure sensing applications. Here, we present a simple sensor design comprising a piece of paper, a graphite pencil, and a copper plate. The proposed fabrication process is simple and eco-friendly. Beyond design and fabrication, our study explores the performance of paper-based sensors in effectively measuring and monitoring pressure changes induced by varying deflection angles. Our findings show that as the deflection angle increases, the sensor exhibits a proportional increase in the relative change in resistance. Furthermore, the practical applicability of the fabricated sensor is demonstrated through real-world testing on a human finger, considering different positions. In essence, our research positions paper-based strain sensors as a promising and practical choice for affordable, eco-friendly, and responsive pressure sensing.

Rapid, low-cost determination of Hg2+, Cu2+, and Fe3+ using a cellulose paper-based sensor and UV–vis method with silver nanoparticles synthesized with S. mammosum

As water effluents are often highly contaminated with metals, having a quick and cost-effective method of analysis is crucial. This study used the supernatant derived from the green synthesis of silver nanoparticles (AgNPs) with Solanum mammosum to detect mercury, copper, and iron with a low-cost cellulose paper-based sensor and a rapid colorimetric method applying ultraviolet–visible spectroscopy (UV–Vis). AgNPs in two precursor concentrations using silver nitrate, 1 mM (17.4 ± 9 nm) and 50 mM (and 22 ± 8.1 nm), were utilized to assess the efficacy of the analysis and removal of Hg2+, Cu2+, and Fe3+ from contaminated water. Cellulose paper-based sensor showed limits of detection (LODs) for Hg2+ of 2.46 and 123 μM using AgNPs at concentrations of 1 and 50 mM, respectively. For Cu2+, the LODs were 55 and 2750 μM, and for Fe3+, the LODs were 49 and 2470 μM using the respective concentrations. To differentiate and detect the cations with the naked eye, a potassium iodide and potassium ferrocyanide (1:1) aqueous solution was used, producing a yellow, pink, and blue color for Hg2+, Cu2+, and Fe3+, respectively. Additionally, the titration curves of Hg2+, Fe3+, and Cu2+ were examined by UV–Vis using the supernatant liquid. The LODs for the UV–Vis method using AgNPs at a concentration of 1 mM were 1.50 μM for Hg2+, 10.7 μM for Cu2+, and 4.33 μM for Fe3+, while the LODs for AgNPs at 50 mM were 5.75, 27.6, and 15 μM for Hg2+, Cu2+, and Fe3+, respectively. Furthermore, these nanoparticles were utilized to assess the efficacy of the removal of Hg2+, Cu2+, and Fe3+ from contaminated water. Removal efficiency with the solid 50 mM AgNPs was analyzed via flame absorption spectrophotometry; values over 95% were obtained for the three ions. The results underscore the effectiveness of a green synthesis approach to generating AgNPs, enabling efficient and economical cation analysis and water decontamination.

A facile cellulosic paper-based colorimetric sensor for detection of perchlorate using albumin-conjugated gold nanoparticles

Perchlorate, a prevalent and dangerous contaminant, is being increasingly found in untreated wastewater from urban areas and industrial discharges, as well as in unmonitored surface and groundwater sources. The urgent need for the creation of straightforward, efficient, and environmentally friendly sensing techniques to detect perchlorate in water. Cellulosic paper-based sensors show great promise as sustainable tools for detecting chemical pollutants. The study aimed to develop and evaluate the effectiveness of a paper-based sensor for detecting perchlorate levels in water samples. The approach showcased a reliable perchlorate colorimetric detection method, integrating digital smartphone imagery with paper-based sensors. The sensor employs a colorimetric assay that relies on the modification of gold nanoparticles with egg albumin protein, a material derived from biological sources. A digital smartphone facilitates on-site colorimetric data collection, and image processing methods are used to determine the presence of perchlorate in water samples based on these digital pictures. The grayscale color intensity derived from digital images is utilized for quantitative analysis. Comprehensive parametric evaluations were conducted to examine the stability and selectivity of the color intensities obtained from the sensor. The limits of detection and quantification are established at 2.86 µg/L and 9.55 µg/L, respectively. This study delivers a facile, highly sensitive, and cost-effective technique for the detection of perchlorate, particularly advantageous in industrial and rural settings where advanced detection devices are scarce.

Ln-MOFs with in-situ exsolved perovskite as ratiometric fluorescent for H2O and Cu2+: Spacial charge transfer and detection mechanism

Herein, a ratiometric fluorescent sensor based on CPB⊆Pb/Eu-MOF heterojunction has been designed for rapid, sensitive and visual detection of H2O and Cu2+ in extraction solution. The energy transfer from Pb2+ to Eu3+ in Pb/Eu-MOF has enhanced the luminescent emission of Eu3+, and the CPB⊆Pb/Eu-MOF n-n heterojunction with S-scheme charge transfer can stabilize CPB to activate the detecting for H2O and Cu2+. In-situ XPS and XRD have confirmed the phase transformation from cubic CPB to CsPb2Br5 majorly contributes to color switch when being introduced by H2O. Moreover, the dynamic quenching and electron transfer are verified by the adsorption energy Br-Cu bonding according to DFT calculation and the shortened fluorescence lifetime. Typically, 0.2CPB⊆Pb/Eu-MOF composite exhibits a highly sensitive and selective ratiometric fluorescent sensing. The proper linear ranges from 10.80 % to 23.10 % and a low detection limit of 0.26 % for H2O, while 20–180 μM, R2 = 0.996, and 8.09 μM for Cu2+. More importantly, the paper-based sheet sensor has been manufactured practically in the real floral teas and different solvents for the visual detection of H2O and Cu2+ by naked eyes.

Flexible cellulose paper-based biosensor from inkjet printing for non-invasive glucose monitoring

Wearable glucose sensors have attracted significant attention for enabling non-invasive blood glucose measurement without discomfort and risk of infection. However, it is a challenge to simultaneously realize wearable adaptability, biodegradability, and excellent sensing performance. Herein, a cellulose paper-based non-invasive biosensor relying on reverse iontophoresis was designed to detect glucose in interstitial fluid (ISF), and two different enzyme immobilization strategies have been compared. The results showed inkjet-printed cellulose paper-based biosensor (IPB) performances better than the drop-coated cellulose paper-based biosensor (DPB). IPB has twice response current more than DPB in detection range (0–10 mM). In sensitivity, IPB is 1.170 μA/mM three times higher than the DPB (0.376 μA/mM). Besides, IPB's electron-transfer resistance (Rct) is 7.27 kΩ smaller than DPB (Rct = 10.51 kΩ) about 30 %. More importantly, IPB exhibited a good reproducibility (RSD, 4.82 %), which was much less than DPB (RSD, 18.35 %). Furthermore, the IPB realizes noninvasive continuous glucose monitoring over 6 h in volunteer experiments with great analytical performance comparable to commercial devices (Pearson correlation 0.732). Cellulose paper-based glucose sensors with inkjet printing provide non-invasive access to statistically significant diagnostic information, simple and cost-effective, which promotes the application of flexible, wearable, degradable bioelectrodes in continuous glucose monitoring at home, providing a concept for full integration in a compact and portable way in the future.

A frugal machine-intelligent paper sensor for quantification of glucose through standalone desktop application: A computational and experimental approach

A paper-based electrochemical sensor utilizing MoS2 as sensing material is developed to quantitatively estimate glucose in a complex extracellular fluid matrix. The contribution of MoS2 as sensing material is substantiated in the context of density functional theory formalism. The molecular modelling of MoS2 and glucose interaction is elucidated through the theoretical estimation of non-covalent interactions and charge density difference plots. The charge transfer phenomenon during the oxidation of glucose molecule in electrochemical experiments is verified through electronic band structure analysis and frontier orbital theory. The electrochemical responses indicate that the sensor exhibits an average accuracy of nearly 96%, with a quantification limit of 100 nM. Furthermore, the chronoamperometric measurements highlight the superior sensitivity of the device in presence of various perturbing molecules. The obtained DPV responses were integrated with a robust machine learning-driven standalone app GluQuantify. This app precisely predicts the glucose concentrations in serum samples. The utilization of GluQuantify substantially elevates the overall accuracy of the sensing platform to 99% and automates the detection process. The application also enhances the resolution of the sensor to 0.01 µM, which mitigates the sensor resolution-related issues in manual estimation.

Nanozyme-Catalyzed Colorimetric Detection of the Total Antioxidant Capacity in Body Fluids by Paper-Based Microfluidic Chips.

Total antioxidants play a crucial role in human health, and detection of the total antioxidant capacity (TAC) has broad application prospects in fields such as food safety, environmental assessment, and disease diagnosis. However, a long detection time, cumbersome steps, high cost, reliance on professional equipment, and nonportability still remain significant challenges. In this work, an efficient strategy of point-of-care testing (POCT) of the TAC in body fluids by nanozyme-catalyzed colorimetric paper-based microfluidic sensors is proposed. The paper-based microfluidic sensors coupled with a smartphone can reduce testing costs and provide portability. The nanozyme prepared by the solvothermal method presents Michaelis constants of 0.11 and 0.129 mM for H2O2 and TMB, respectively. A method for immobilizing nanozymes and chromogenic agents on a paper-based microfluidic chip is established. Based on smartphone photography and image grayscale extraction, the TAC can be qualitatively detected with a detection limit and linear range of 33.4 and 50-700 μM, respectively. Furthermore, the proposed sensor can realize the one-step quantitative analysis of the TAC in body fluids (blood, saliva, and sweat) within 15 min. The proposed nanozyme-catalyzed colorimetric paper-based microfluidic sensors presented in this study exhibit promising application prospects in the fields of biochemical analysis and POCT.

Paper-based Electrochemical Sensor Integrated with Gold Nanoparticle-Decorated Carbon Cloth as a Working Electrode for Nitric Oxide Detection in Artificial Tears.

Nitric oxide (NO) in human tears regulates numerous ocular surface processes, such as tear generation, corneal wound healing, conjunctival vascular tone, and so forth. Any deviation from its normal concentration is linked to various ocular syndromes, including microbial keratitis, conjunctivitis, pterygium, dry eye, retinitis, glaucoma, and so forth. Therefore, precise monitoring of NO in tears can be considered as a potential biomarker for ocular diseases. Here, we report a highly sensitive and selective electrochemical NO sensor using carbon ink-based electrodes. Counter, working (WE), and reference electrodes have been designed and painted on a butter paper by using carbon ink. To improve the sensing performance, the WE has been modified with a gold nanoparticle (Au NP)-deposited carbon cloth (CC). Such a paper-based sensor demonstrated high sensitivity of ∼0.34 μA μM-1 cm-2, ultralow detection limit of ∼2.35 nM, wide linear range of 10 nM-0.4 mM, and fast response time (0.35 s). The sensor also showed excellent stability and selectivity toward the interfering agents in human body fluids. Such a low-cost, flexible paper-based sensor was employed for the detection of NO in artificial tears.

A paper-based lateral flow immunochromatographic sensor for the detection of tricyclazole in rice

Tricyclazole is commonly used to prevent rice blast to meet the carbohydrate intake needs of half of the global population, and a large number of toxicological reports indicate that monitoring of tricyclazole is necessary. Here, we analyzed the structure of tricyclazole and designed different hapten derivatization strategies to prepare a high-performance monoclonal antibody (half inhibition concentration of 1.61 ng/mL), and then a lateral flow immunochromatographic sensor based on gold nanoparticles for the detection of tricyclazole in rice, with a limit of detection of 6.74 μg/kg and 13.58 μg/kg in polished and brown rice, respectively. The recoveries in rice were in the range of 84.6–107.4%, no complex pretreatment was required for comparison with LC-MS/MS, and the comparative analysis demonstrated that our method had good accuracy and precision. Therefore, the developed lateral flow immunochromatographic analysis was a reliable and rapid means for the on-site analysis of tricyclazole in rice.

Versatile Solvatochromic fluorophores based on Schiff bases for colorimetric detection of metal ions

In recent years, fluorescent probes have been extensively studied as powerful tools for the effective assessment of toxic metal ions due to their high sensitivity, selectivity, capability for real-time and non-invasive monitoring, and versatility. In this paper, novel fluorescent probes based on Schiff bases, namely 2-((1E,2E)-1-(6-chlorobenzo[d]thiazol-2-ylimino)-3-(4-(dimethylamino)phenyl)allyl)phenol (1) and 2-((1E,2E)-3-(4-(dimethylamino)phenyl)-1-(4-methylbenzo[d]thiazol-2-ylimino)allyl)phenol (2), were synthesized and characterized. The optical properties of these probes were examined across a spectrum of fourteen solvents with varying polarities, revealing significant solvatochromic effects on both absorption and fluorescence spectra. The analysis delineated a discernible difference in dipole moment between electronic ground and excited states, with molecules exhibiting enhanced stabilization in singlet excited states. Subsequently, a straightforward method was devised for the selective and sensitive detection of diverse metal ions in aqueous solutions, including K+, V3+, Cr3+, Fe3+, Co2+, Ni2+, Cu2+, Se6+, Cd2+, Ba2+, and Hg2+, through naked eye observation, UV–Visible, and fluorimetric measurements. Notably, the UV–Vis spectra of probes 1 and 2 manifested a significant red shift upon the addition of metal ions, indicative of potential ligand-to-metal charge-transfer (LMCT) phenomena, with the exception of Ni2+, Cu2+, and Se6+ions. The observed alterations in optical absorption and fluorescence emission contributed to the probes' heightened selectivity and sensitivity, obviating the necessity for sample pretreatment. Competitive assays underscored the probes' preference for Cr3+ and V3+ ions over other common metal ions. Furthermore, Job's plot analysis suggested a 1:1 ligand-to-metal molar ratio binding. The investigated Schiff bases exhibited elevated binding constants (Ka), low detection limits, and limits of quantification, alongside diminished fluorescence quantum yield. Leveraging fluorescence quenching, facile paper-based sensor strips coated with Schiff bases facilitated prompt, qualitative, and quantitative in situ detection of metal ions in aqueous solutions across a broad concentration spectrum, discernible to the naked eye under UV light.

Paper based analytical devices for ions determination in nasal secretions demonstrating association with olfactory function

Nasal ions environment plays a crucial role in maintaining nasal physiology and supports olfactory transmission. Addressing the limited research on nasal ion levels and their association with olfactory function, paper-based sensors were developed for determination of sodium, potassium, calcium and chloride in the nasal mucus of healthy volunteers and patients with olfactory dysfunction. Multi-walled carbon nanotubes and carbon quantum dots from beetroot were incorporated into paper substrate where sensors were designed with ion association complexes for sodium, potassium, calcium and chloride enhancing the recognition sensing capabilities. The sensors composition was optimized, including ion-exchange materials and plasticizers, to enhance sensitivity and selectivity. The performance of the sensors is evaluated based on Nernstian slope, dynamic range, detection limit and response time. Selectivity of the sensors was tested and the results demonstrated high selectivity for the target ions. The sensors were successfully determined sodium, potassium, calcium and chloride levels in nasal mucus of healthy volunteers and patients with olfactory dysfunction. The results revealed elevated calcium levels in patients with olfactory dysfunction, highlighting associated diagnostic implications. This suggests that the proposed sensors could serve as a diagnostic tool for olfactory evaluation, particularly in resource-constrained settings where access to advanced diagnostic tools is limited.

A smartphone-assisted portable on-site detection system for organophosphorus pesticides in vegetables and fruits based on all-in-one paper-based sensors: 2,2-Dichlorovinyl dimethyl phosphate as a model

The improper use of organophosphate pesticides (OPs) can lead to residue posing a serious threat to human health and environment. Therefore, the development of a simple, portable, and sensitive detection method is crucial. Herein, a bioenzyme-nanozyme-chromogen all-in-one paper-based sensor was synthesized. Initially, the Ce/Zr-MOF with peroxidase-like activity was grown on filter paper (FP) using in-situ solvent thermal method, resulting in Ce/Zr-MOF@FP. Subsequently, the AChE-ChO-TMB system was immobilized onto Ce/Zr-MOF@FP using biocompatible gelatin, which enhanced cascade catalysis efficiency through the proximity effect. Based on the inhibition principle of OPs on AChE, we integrated this sensor with Python-based image recognition algorithm to achieve detection of OPs. Using 2,2-dichlorovinyl dimethyl phosphate (DDVP) as a model of OPs, it has good detection performance with a detection limit of 0.32 ng mL−1 and a recovery rate range of 95–107%. The potential for on-site detection of DDVP residues in vegetables and fruit samples is highly promising.

An ultrasensitive paper-based SERS sensor for detection of nucleolin using silver-nanostars, plastic antibodies and natural antibodies

A state-of-the-art, ultrasensitive, paper-based SERS sensor has been developed using silver nanostars (AgNSs) in combination with synthetic and natural antibodies. A key component of this innovative sensor is the plastic antibody, which was synthesized using molecularly imprinted polymer (MIP) technology. This ground-breaking combination of paper substrates/MIPs with AgNSs, which is similar to a sandwich immunoassay, is used for the first time with the aim of SERS detection and specifically targets nucleolin (NCL), a cancer biomarker. The sensor device was carefully fabricated by synthesizing a polyacrylamide-based MIP on cellulose paper (Whatman Grade 1 filter) by photopolymerization. The binding of NCL to the MIP was then confirmed by natural antibody binding using a sandwich assay for quantitative SERS analysis. To facilitate the detection of NCL, antibodies were pre-bound to AgNSs with a Raman tag so that the SERS signal could indicate the presence of NCL. The composition of the sensory layers/materials was meticulously optimized. The intensity of the Raman signal at ∼1078 cm−1 showed a linear trend that correlated with increasing concentrations of NCL, ranging from 0.1 to 1000 nmol L−1, with a limit of detection down to 0.068 nmol L−1 in human serum. The selectivity of the sensor was confirmed by testing its analytical response in the presence of cystatin C and lysozyme. The paper-based SERS detection system for NCL is characterized by its simplicity, sustainability, high sensitivity and stability and thus embodies essential properties for point-of-care applications. This approach is promising for expansion to other biomarkers in various fields, depending on the availability of synthetic and natural antibodies.

Inductive Paper-Based Flexible Contact Force Sensor Utilizing Natural Micro-Nanostructures of Paper: Simplicity, Economy, and Eco-Friendliness.

Inductive contact force sensors, known for their high precision and anti-interference capabilities, hold significant potential applications in fields such as wearable and medical monitoring devices. Most of the current research on inductive contact force sensors employed novel nanomaterials as sensitive elements to enhance their sensitivity and other performance characteristics. However, sensors developed through such methods typically involve complex preparation processes, high costs, and difficulty in biodegradation, which limit their further development. This article introduces a new flexible inductive contact force sensor using paper as a sensitive element. Paper inherently possesses micro- and nanostructures on its surface and interior, enabling it to sensitively convert changes in contact force into changes in displacement, making it suitable for use as the sensor's sensitive element. Additionally, the advantages of paper also include its great flexibility, low cost, wide availability, and biodegradability. Performance testing on this flexible sensor showed good repeatability, hysteresis, sensitivity, and consistency. When used in experiments for monitoring human motion and respiration, this sensor also exhibited great detection performance. The proposed inductive paper-based flexible contact force sensor, with its simple structure, easy manufacturing process, cost-effectiveness, eco-friendliness, and good sensing performance, provides new insights into research for contact force sensors.

Nanozyme-Inhibited SERS Multichannel Paper-Based Sensor Array for the Quantification and Identification of Biothiols and Cancer Cells Based on Three Ag-Based Nanomaterials.

Biothiols play essential roles in maintaining normal physiological functions, resisting oxidative stress, and protecting cell health. Establishing an effective and reliable sensor array for the accurate quantification and discrimination of diverse biothiols is extremely meaningful. In this work, Ag/Mn3O4, Ag3PO4, and Ag3Cit with excellent oxidase-mimetic activity and surface-enhanced Raman scattering (SERS)-enhanced features have been prepared and loaded onto Whatman filter paper (WFP) to build SERS paper chips as three sensing channels, which can induce 3,3',5,5'-tetramethylbenzidine (TMB) oxidation to SERS-active reporters (TMBox) and concurrently generate prominent SERS signals. Nevertheless, the addition of biothiols can suppress conversion from TMB to TMBox, which can cause the reduction of the SERS signal from TMBox. Interestingly, each SERS sensing channel can generate different TMBox signals' variations due to differences in the oxidative inhibition abilities of diverse biothiols and exclusive properties of each paper chip, which can be plotted as specific fingerprint patterns of each biothiol and further translated into intuitive two-dimensional (2D) clustering profiles through linear discriminant analysis (LDA) and hierarchical cluster analysis (HCA) techniques for precise identification of these six biothiols with the minimum concentration of 1 μM. More importantly, this SERS sensor array is exploited for the precise quantification of intracellular glutathione (GSH), and can differentiate between normal and cancer cells based on different intracellular GSH contents and even identify different types of tumor cells, demonstrating its powerful application prospects in disease diagnosis.

Emerging techniques for the trace elemental analysis of plants and food-based extracts: A comprehensive review

This comprehensive review investigates the dynamic landscape of trace elemental analysis methodologies applied to plants and food-based extracts. The exploration spans from the inception of techniques to the latest procedures, contributing to heightened precision and sensitivity in elemental detection. According to the WHO, herbal plants and medicine from varied soil compositions serve as crucial therapeutic agents for 70–80 % of the world's population. Yet, their susceptibility to trace element toxicity poses a significant risk to human health. Rising population and increased food demands have led to environmental pollution, contaminating the food chain through unintended activities like industrialization, mining, and pesticide production. The elemental composition of plants and derived extracts is central to comprehending nutritional profiles, evaluating product quality, and ensuring food safety. Methodological advancements, progressing from manual procedures to sophisticated technologies such as X-ray fluorescence (XRF), neutron activation analysis (NAA), inductively coupled plasma optical emission spectroscopy (ICP OES), and inductively coupled plasma mass spectrometry (ICP-MS), are delineated. Recent strides in paper-based electrochemical sensors are highlighted for their distinctive capabilities and elucidation of associated advantages and limitations.Moreover, the review delves into innovative sample preparation methodologies, encompassing microwave-assisted digestion and solid-phase microextraction, to amplify the efficiency of elemental extraction and subsequent analysis. Integrating data analytics and machine learning in elucidating complex elementary datasets is explored, underscoring the potential for heightened accuracy and automation in trace elemental analysis. This review compiles literature data, summarizing sample preparation methods for various herbal parts (roots, soil, stems, bark, fruits, food). Standard protocols from WHO, United States Pharmacopeia-National Formulary (USP-FR), Ayurveda, Yoga and Naturopathy, Unani, Siddha, and Homeopathy (AYUSH) are considered. Lead, Cadmium, Mercury, and Arsenic are the primary toxic elements of concern in herbal medicines. This review furnishes valuable insights tailored for researchers, analysts, and policymakers actively involved in advancing the domain of trace elemental analysis in plants and food-based extract.

Interlayer cross-linked MXene enables ultra-stable printed paper-based flexible sensor for real-time humidity monitoring

With an abundance of hydrophilic active sites present on the surfaces, MXene exhibits significant potential for application in the field of humidity monitoring. Nevertheless, achieving the high response intensity, excellent response sensitivity, structural stability, and oxidation resistance in the MXene-based humidity sensors remains a formidable challenge. Herein, we propose a humidity sensor made from the paper-based flexible sensor with copper electrode and polyethyleneimine/silver nitrate cross-linking modified MXene composite materials. The humidity sensor prepared in this work presents a satisfactory capacitance response rate (819.9 % in 97 % RH) and favorable sensitivity (6.9/11.9 s for response/recovery time). Meanwhile, the humidity sensor possesses outstanding structural stability (less than 3 % attenuation of the capacitance response after 100 bending cycles) and superior oxidation resistance. Moreover, the real-time humidity monitor assembled based on the humidity sensor has realized the effective monitoring of human skin humidity and dynamic respiration. Consequently, this study provides a viable approach for achieving reliable real-time humidity monitoring, demonstrating significant potential in the realms of intelligent actuators, sensing devices, and health care.

Paper-based disposable electrochemical sensor from readily available materials for cost-effective triclosan detection

This study introduces a disposable electrochemical sensor fabricated from readily available low-cost materials. The design features a three-electrode electrochemical cell made of a simple graphite dry lubricant and silicone sealant composite, screen-printed onto a sulphite paper substrate. The ideal composite mixture was stablished through factorial design. The sensors were applied to the electroanalytical detection of triclosan, an antimicrobial agent used in personal care products, with concerns about its impact on ecosystems and human health. A subsequent factorial design determined the optimal voltammetric conditions. This approach yielded a method with limits of detection and quantification of 0.05 μmol L–1 and 0.17 μmol L–1, respectively, with a linear range from 0.20 μmol L–1 to 10.30 μmol L–1 for triclosan. The method was successfully applied to analyze triclosan in tap water and personal care products, including toothpaste, mouthwash, and liquid soap, achieving recovery rates ranging from 96 % to 118 %.