Graphene-polyaniline modified electrochemical droplet-based microfluidic sensor for high-throughput determination of 4-aminophenol

Molecular imprinting technology for biomedical applications

Molecularly imprinted polymers (MIPs), a type of biomimetic material, have attracted considerable interest owing to their cost-effectiveness, good physiochemical stability, favourable specificity and selectivity for target analytes, and widely used for various biological applications. It was demonstrated that MIPs with significant selectivity towards protein-based targets could be applied in medicine, diagnostics, proteomics, environmental analysis, sensors, various in vivo and/or in vitro applications, drug delivery systems, etc. This review provides an overview of MIPs dedicated to biomedical applications and insights into perspectives on the application of MIPs in newly emerging areas of biotechnology. Many different protocols applied for the synthesis of MIPs are overviewed in this review. The templates used for molecular imprinting vary from the minor glycosylated glycan-based structures, amino acids, and proteins to whole bacteria, which are also overviewed in this review. Economic, environmental, rapid preparation, stability, and reproducibility have been highlighted as significant advantages of MIPs. Particularly, some specialized MIPs, in addition to molecular recognition properties, can have high catalytic activity, which in some cases could be compared with other bio-catalytic systems. Therefore, such MIPs belong to the class of so-called 'artificial enzymes'. The discussion provided in this manuscript furnishes a comparative analysis of different approaches developed, underlining their relative advantages and disadvantages highlighting trends and possible future directions of MIP technology.

Novel solid inks based on beeswax, graphite and graphene applied to the fabrication of paper-based sensor for galactose determination

In this study, we present for the first time a simple and novel method for the fabrication of paper-based electrochemical sensors. The device development was carried out in a single stage with a standard wax printer. Hydrophobic zones were delimited with commercial solid ink, while electrodes were generated using new composite solid inks of graphene oxide/graphite/beeswax (GO/GRA/beeswax) and graphite/beeswax (GRA/beeswax). Subsequently, the electrodes were electrochemically activated by applying an overpotential. Various experimental variables for the GO/GRA/beeswax composite synthesis and electrochemical system obtention were evaluated. The activation process was examined by SEM, FTIR, cyclic voltammetry, electrochemical impedance spectroscopy and contact angle measurement. These studies showed morphological and chemical changes in the electrode active surface. As a result, the activation stage considerably improved the electron transfer on the electrode. The manufactured device was successfully applied for galactose (Gal) determination. This method presented a linear relation in the Gal concentration range from 84 to 1736 μmol L^-1, with a LOD of 0.1 μmol L^-1. The variation within and between-assay coefficients were 5.3% and 6.8%, respectively. The strategy here exposed for paper-based electrochemical sensors design is an unprecedented alternative system and represents a promising tool for mass production of economic analytical devices.

A carbon based-screen-printed electrode amplified with two-dimensional reduced graphene/Fe3O4 nanocomposite as electroanalytical sensor for monitoring 4-aminophenol in environmental fluids

The analysis water pollutants are so important strategy for investigation of water quality. On the other hand, 4-aminophenol is known as a hazardous and high-risk compound for humans, and its detection and measurement is very important for investigating the quality of surface and groundwater. In this study, graphene/Fe₃O₄ nanocomposite was synthesized by a simple chemical method and characterized by EDS and TEM methods and results showed Nano spherical shape of Fe₃O₄ nanoparticle with diameter about 20 nM decorated at surface of 2D reduce graphene nanosheet (2D-rG-Fe₃O₄). The 2D-rG-Fe₃O₄ was used as excellent catalyst at surface of carbon-based screen-printed electrode (CSPE) and used as electroanalytical sensor in monitoring and determination of 4-aminophenol in waste water sample. The results confirmed improving ∼4.0 times in oxidation signal and reducing 120 mV in oxidation potential of 4-aminophenol at surface of 2D-rG-Fe₃O₄/CSPE compare to CSPE, respectively. The electrochemical investigation showed pH dependence behavior with equal value of electron and proton for -aminophenol at surface of 2D-rG-Fe₃O₄/CSPE. Using square wave voltammetry method (SWV), the 2D-rG-Fe₃O₄/CSPE successfully monitored 4-aminophenol in the concentration range 1.0 nM-200 μM. Finally, 2D-rG-Fe₃O₄/CSPE monitored 4-aminophenol in the different environmental fluids such as urban waste water, industrial waste water and river samples with recovery range 97.2%-104.3% that confirm powerful ability of 2D-rG-Fe₃O₄/CSPE as analytical tool.

A bibliometric analysis of graphene in acetaminophen detection: Current status, development, and future directions

Acetaminophen is a widely used analgesic throughout the world. Detection of acetaminophen has particular value in pharmacy and clinics. Electrochemical sensors assembled with advanced materials are an effective method for the rapid detection of acetaminophen. Graphene-based carbon nanomaterials have been extensively investigated for potential analytical applications in the last decade. In this article, we selected papers containing both graphene and acetaminophen. Bibliometrics was used to analyze the relationships and trends among these papers. The results show that the topic has grown at a high rate since 2009. Among them, the detection of acetaminophen by an electrochemical sensor based on graphene is the most important direction. Graphene has moved from being a primary sensing material to a substrate for immobilization of other active ingredients. In addition, the degradation of acetaminophen using graphene-modified electrodes is also an important direction. We analyzed the research history and current status of this topic through bibliometrics. Authors, institutions, countries, and key literature were discussed. We also proposed perspectives for this topic.

Development of molecularly imprinted polymer based phase boundaries for sensors design (review)

Achievements in polymer chemistry enables to design artificial phase boundaries modified by imprints of selected molecules and some larger structures. These structures seem very useful for the design of new materials suitable for affinity chromatography and sensors. In this review, we are overviewing the synthesis of molecularly imprinted polymers (MIPs) and the applicability of these MIPs in the design of affinity sensors. Such MIP-based layers or particles can be used as analyte-recognizing parts for sensors and in some cases they can replace very expensive compounds (e.g.: antibodies, receptors etc.), which are recognizing analyte. Many different polymers can be used for the formation of MIPs, but conducing polymers shows the most attractive capabilities for molecular-imprinting by various chemical compounds. Therefore, the application of conducting polymers (e.g.: polypyrrole, polyaniline, polythiophene, poly(3,4-ethylenedioxythiophene), and ortho-phenylenediamine) seems very promising. Polypyrrole is one of the most suitable for the development of MIP-based structures with molecular imprints by analytes of various molecular weights. Overoxiation of polypyrrole enables to increase the selectivity of polypyrrole-based MIPs. Methods used for the synthesis of conducting polymer based MIPs are overviewed. Some methods, which are applied for the transduction of analytical signal, are discussed, and challenges and new trends in MIP-technology are foreseen.

Electrochemically Deposited Molecularly Imprinted Polymer-Based Sensors

This review is dedicated to the development of molecularly imprinted polymers (MIPs) and the application of MIPs in sensor design. MIP-based biological recognition parts can replace receptors or antibodies, which are rather expensive. Conducting polymers show unique properties that are applicable in sensor design. Therefore, MIP-based conducting polymers, including polypyrrole, polythiophene, poly(3,4-ethylenedioxythiophene), polyaniline and ortho-phenylenediamine are frequently applied in sensor design. Some other materials that can be molecularly imprinted are also overviewed in this review. Among many imprintable materials conducting polymer, polypyrrole is one of the most suitable for molecular imprinting of various targets ranging from small organics up to rather large proteins. Some attention in this review is dedicated to overview methods applied to design MIP-based sensing structures. Some attention is dedicated to the physicochemical methods applied for the transduction of analytical signals. Expected new trends and horizons in the application of MIP-based structures are also discussed.

Electrochemical pH regulation in droplet microfluidics

We report a method for electrochemical pH regulation in microdroplets generated in a microfluidic device. The key finding is that controlled quantities of reagents can be generated electrochemically in moving microdroplets confined within a microfluidic channel. Additionally, products generated at the anode and cathode can be isolated within descendant microdroplets. Specifically, ∼5 nL water-in-oil microdroplets are produced at a T-junction and then later split into two descendant droplets. During splitting, floor-patterned microelectrodes drive water electrolysis within the aqueous microdroplets to produce H⁺ and OH^-. This results in a change in the pHs of the descendant droplets. The droplet pH can be regulated over a range of 5.9 to 7.7 by injecting controlled amounts of charge into the droplets. When the injected charge is between -6.3 and 54.5 nC nL^-1, the measured pH of the resulting droplets is within ±0.1 pH units of that predicted based on the magnitude of the injected charge. This technique can likely be adapted to electrogeneration of other reagents within microdroplets.

Development of an Efficient Voltammetric Sensor for the Monitoring of 4-Aminophenol Based on Flexible Laser Induced Graphene Electrodes Modified with MWCNT-PANI

Sensitive electrodes are of a great importance for the realization of highly performant electrochemical sensors for field application. In the present work, a laser-induced carbon (LIC) electrode is proposed for 4-Aminophenol (4-AP) electrochemical sensors. The electrode is patterned on a commercial low-cost polyimide (Kapton) sheet and functionalized with a multi-walled carbon nanotubes polyaniline (MWCNT-PANI) composite, realized by an in-situ-polymerization in an acidic medium. The LIC electrode modified with MWCNT-PAPNI nanocomposite was investigated by SEM, AFM, and electrochemically in the presence of ferri-ferrocyanide [Fe(CN)₆]^3−/4− by cyclic voltammetry and impedance spectroscopy. The results show a significant improvement of the electron transfer rate after the electrode functionalization in the presence of the redox mediators [Fe(CN)₆]^3−/4−, related directly to the active surface, which itself increased by about 18.13% compared with the bare LIG. The novel electrode shows a good reproducibility and a stability for 20 cycles and more. It has a significantly enhanced electro-catalytic activity towards electrooxidation reaction of 4-AP inferring positive synergistic effects between carbon nanotubes and polyaniline PANI. The presented electrode combination LIC/MWCNT-PANI exhibits a detection limit of 0.006 μM for the determination of 4-AP at concentrations ranging from 0.1 μM to 55 μM and was successfully applied for the monitoring in real samples with good recoveries.

Graphene nanosheet-sandwiched platinum nanoparticles deposited on a graphite pencil electrode as an ultrasensitive sensor for dopamine

An ultra-sensitive sensor of dopamine is introduced. The sensor is constructed by encapsulating platinum nanoparticles (PtNPs) between reduced graphene oxide (GR) nanosheets. The sandwiched PtNPs between GR layers acted as a spacer to prevent aggregation and provided a fine connection between the GR nanosheets to provide fast charge transfer. This specific orientation of the GR nanosheets and PtNPs on the graphite pencil electrode (GPE) substantially improved the electrocatalytic activity of the sensor. The synthesized graphene oxide and the fabricated sensor were comprehensively characterized by Fourier-transform infrared spectroscopy (FTIR), Raman spectroscopy, field emission-scanning electron microscopy (FE-SEM), electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV), and square wave voltammetry (SWV). The value of the charge transfer coefficient (α), apparent heterogeneous electron transfer rate constant (k_s), and electroactive surface area for dopamine were found to be about 0.57, 8.99 s⁻¹, and 0.81 cm², respectively. The developed sensor is highly sensitive towards dopamine, and the detection limit is 9.0 nM. The sensor response is linear for dopamine concentration from 0.06 to 20 μM (R² = 0.9991). The behavior of the sensor for dopamine in the presence of a high concentration of l(+) Ascorbic acid and other potential interferents was satisfactory. High recovery percentage between 90% and 105% in the human urine sample, good reproducibility, and facile fabrication of the electrode make it a good candidate for dopamine sensing.

An efficient, highly sensitive, and selective electrochemical sensor using PtNPs sandwiched graphene layered modified graphite pencil electrode.

A bi-functionalized metal-organic framework based on N-methylation and Eu3+ post-synthetic modification for highly sensitive detection of 4-Aminophenol (4-AP), a biomarker for aniline in urine

4-Aminophenol (4-AP), which is a biomarker of aniline and represents the internal dose of aniline exposure in the human body, has attracted much attention for its detection in recent years. In this work, a bi-functionalized luminescent metal-organic framework (MOF), Eu@MOF-253-CH_3, is designed and prepared through encapsulating the methyl groups and the Eu³⁺ cations into MOF-253 based on post-synthetic modification strategy. This study shows that the bi-functionalized Eu@MOF-253-CH₃ can specifically recognize 4-AP upon luminescence quenching, while refraining from the interference of other coexisting species in urine. The Eu@MOF-253-CH₃ hybrid as a 4-AP sensor also displays excellent performances including high water tolerance, good pH-independent stability, fast response, great selectivity and elevated sensitivity (0.5 μg mL^-1) attributed to N-viologenized ligand. These results suggest the bi-functionalized Eu@MOF-253-CH₃ can act as a promising sensor to practically monitor 4-AP's concentrations in human urine system, and then to realize the screening and pre-diagnosis of human health. Moreover, the possible sensing mechanisms are further explored at length.

2D Co3O4 stabilizing Rh nano composites developed for visual sensing bioactive urea and toxic p-aminophenol in practice by synergetic-reinforcing oxidase activity

To enlarge the perspective of nanozyme, 2-dimensional Co₃O₄ stabilizing Rh nano composite (2D Co₃O₄@Rh NC) was identified and developed first by one-pot surfactant-aided oxido-reduction. By virtue of the synergetic-reinforcing oxidase activity between 2D Co₃O₄ substrate and Rh nano particles, the obtained 2D Co₃O₄@Rh NC could catalyze the oxidation of chromogenic substrate 3,3',5,5,'-tetramethylbenzidine (TMB) to blue oxTMB with quite a low Michaelis-Menten constant (K_m) of 0.018 mM and a quick v_max of 6.45 × 10^-8 M s^-1, expressing superior oxidase-like catalysis with a wide temperature range from 20 to 60 °C. Importantly, either bioactive urea or toxic p-aminophenol (p-Ap) could exclusively alter the existed state of oxTMB with differentiable color changes. Under the optimized conditions, 2D Co₃O₄@Rh NC was successfully applied for ratiometric colorimetric sensing urea and p-Ap in environmental water, soil and urine samples with low detection limits (1.1 μM for urea and 0.68 μM for p-Ap) and satisfactory recoveries (96.0-105.8%). The synergetic enhanced oxidase-like activity of 2D Co₃O₄@Rh NC and the different reaction mechanisms of the 2D Co₃O₄@Rh NC-TMB system to urea and p-Ap were investigated. Not only does the work provide an efficient way for sensing organic pollution of p-Ap, it will offer an efficient potential for diagnosing urea-related diseases on clinical medical testing in future.

Electrochemical assessments of droplet contents in microfluidic channels. Application to the titration of heterogeneous droplets

Series of aqueous droplets containing redox species were generated on-demand in a microfluidic channel and detected downstream by an electrochemical cell. Depending on the cell geometry, amperometric detections were performed to simultaneously determine the velocity, volume and content of circulating droplets in oil. Volumes and velocities were estimated from specific transition times on the chronoamperometric responses, while charge were evaluated from current integration. The results showed that the total charge within droplets was controlled by the geometry of the electrochemical cell and droplet velocity, leading to accurate determinations of droplet content under specific operating conditions. An active merging of droplets with titrating solutions was tested for analytical purposes. The results demonstrated that even if the mixing was not complete during detection, the assessment of droplet content was still valid. The performance of electrochemical detection was thus evidenced to determine the content of heterogeneous droplets. This property is pertinent since the design of sophisticated circuits is no longer required to fully homogenize the droplet content before characterization, opening broader perspectives in droplet-based microfluidics.

Advances in Molecularly Imprinted Polymers Based Affinity Sensors (Review)

Recent challenges in biomedical diagnostics show that the development of rapid affinity sensors is very important issue. Therefore, in this review we are aiming to outline the most important directions of affinity sensors where polymer-based semiconducting materials are applied. Progress in formation and development of such materials is overviewed and discussed. Some applicability aspects of conducting polymers in the design of affinity sensors are presented. The main attention is focused on bioanalytical application of conducting polymers such as polypyrrole, polyaniline, polythiophene and poly(3,4-ethylenedioxythiophene) ortho-phenylenediamine. In addition, some other polymers and inorganic materials that are suitable for molecular imprinting technology are also overviewed. Polymerization techniques, which are the most suitable for the development of composite structures suitable for affinity sensors are presented. Analytical signal transduction methods applied in affinity sensors based on polymer-based semiconducting materials are discussed. In this review the most attention is focused on the development and application of molecularly imprinted polymer-based structures, which can replace antibodies, receptors, and many others expensive affinity reagents. The applicability of electrochromic polymers in affinity sensor design is envisaged. Sufficient biocompatibility of some conducting polymers enables to apply them as "stealth coatings" in the future implantable affinity-sensors. Some new perspectives and trends in analytical application of polymer-based semiconducting materials are highlighted.

Flow-based System: A Highly Efficient Tool Speeds Up Data Production and Improves Analytical Performance

In this review, we cite references from the period between 2015 and 2020 related to the use of a flow-based system as a tool to obtain a modern analytical system for speeding up data production and improving performance. Based on a great deal of concepts for automatic systems, there are several research groups introduced in the development of flow-based systems to increase sample throughput while retaining the reproducibility and repeatability as well as to propose new platforms of flow-based systems, such as microfluidic chip and paper-based devices. Additionally, to apply a developed system for on-site analysis is one of the key features for development. We believe that this review will be very interested and useful for readers because of its impact on developing novel analytical systems. The content of the review is categorized following their applications including quality control and food safety, clinical diagnostics, environmental monitoring and miscellaneous.

Conducting Polymers in the Design of Biosensors and Biofuel Cells

Fast and sensitive determination of biologically active compounds is very important in biomedical diagnostics, the food and beverage industry, and environmental analysis. In this review, the most promising directions in analytical application of conducting polymers (CPs) are outlined. Up to now polyaniline, polypyrrole, polythiophene, and poly(3,4-ethylenedioxythiophene) are the most frequently used CPs in the design of sensors and biosensors; therefore, in this review, main attention is paid to these conducting polymers. The most popular polymerization methods applied for the formation of conducting polymer layers are discussed. The applicability of polypyrrole-based functional layers in the design of electrochemical biosensors and biofuel cells is highlighted. Some signal transduction mechanisms in CP-based sensors and biosensors are discussed. Biocompatibility-related aspects of some conducting polymers are overviewed and some insights into the application of CP-based coatings for the design of implantable sensors and biofuel cells are addressed. New trends and perspectives in the development of sensors based on CPs and their composites with other materials are discussed.

Functional Polymers Structures for (Bio)Sensing Application-A Review

In this review we present polymeric materials for (bio)sensor technology development. We focused on conductive polymers (conjugated microporous polymer, polymer gels), composites, molecularly imprinted polymers and their influence on the design and fabrication of bio(sensors), which in the future could act as lab-on-a-chip (LOC) devices. LOC instruments enable us to perform a wide range of analysis away from the stationary laboratory. Characterized polymeric species represent promising candidates in biosensor or sensor technology for LOC development, not only for manufacturing these devices, but also as a surface for biologically active materials' immobilization. The presence of biological compounds can improve the sensitivity and selectivity of analytical tools, which in the case of medical diagnostics is extremely important. The described materials are biocompatible, cost-effective, flexible and are an excellent platform for the anchoring of specific compounds.

A sensitive sensor based on MOFs derived nanoporous carbons for electrochemical detection of 4-aminophenol

A novel electrochemical sensor based on zinc oxide/nitrogen doped porous carbons (ZnO/NPC) modified electrode has been constructed for detecting 4-aminophenol (4-AP). The ZnO/NPC material was synthesized by one-step carbonization of MOF-5-NH₂. The modified glassy carbon electrode (ZnO/NPC/GCE) holds excellent electrocatalytic activity toward 4-AP, with a sensitivity of about 31.02 μA/μM/cm². Under optimal conditions, its oxidation peak current increases linearly with the increasing concentration of 4-AP (from 5 to 120 μmol/L), and the detection limits is 0.014 μmol/L (S/N = 3). Furthermore, favorable selectivity, superior reproducibility and outstanding stability have been achieved. The ZnO/NPC/GCE has been applied in detecting 4-AP in industrial waste water and achieved positive results with the recovery of 4-AP ranging from 94.02% to 107.7%, which confirms that this sensor is a reliable platform for the detection of 4-AP in waste water.

Simultaneous detection of paracetamol and 4-aminophenol at nanomolar levels using biocompatible cysteine-substituted phthalocyanine

Extension of the conjugation and biocompatibility of the phthalocyanine molecule is expected to improve its stability and interaction with bio-molecules without any fouling.

Platinized agarose microspheres as a new modifier in graphite paste electrodes for the electrochemical determination of 4-aminophenol

In the environment, 4-aminophenol (4-AP) is present as a highly toxic compound and water pollutant. In this study, platinized agarose microspheres (PtAM) were used for the first time, for the preparation of a novel, modified graphite paste electrode (GPE/PtAM) for the electrochemical determination of 4-AP. PtAM was characterized using transmission electron microscopy, field emission scanning electron microscopy and energy dispersive X-ray analysis. The electrochemical response characteristics of GPE/PtAM towards 4-AP were investigated via electrochemical impedance spectroscopy, cyclic voltammetry, differential pulse voltammetry and chronoamperometry. The value of the charge transfer resistance obtained for GPE/PtAM was 27.3 Ω. Microscopic surface areas and the surface concentration of the electroactive species for GPE/PtAM were calculated to be 0.077 cm² and 1.13 × 10⁻³ mol cm⁻², respectively. The electron transfer coefficient, diffusion coefficient and standard heterogeneous rate constants of 4-AP were calculated as 0.274, 4.56 × 10⁻⁴ cm² s⁻¹, and 3.32 × 10⁻¹ cm s⁻¹, respectively. The influence of pH on the oxidation of 4-AP was investigated and a pH value of 2.0 (using a phosphate buffer solution) was selected as the optimum pH. Under optimum conditions, the calibration was linear between 0.8 and 87 μM with a detection limit of 45 nM. Moreover, GPE/PtAM was applied to determine the concentrations of 4-AP in water samples with satisfactory results.

In the environment, 4-aminophenol (4-AP) is present as a highly toxic compound and water pollutant.

A Facile In-Situ Development of L-Valine Film onto the Surface of Carbon Paste Electrode Towards the Detection of Environmentally Hazardous 4-Amino Phenol

A small scale of environmentally hazardous 4-aminophenol can show significant impact on human health. Hence, in the present work, we have designed L-Valine film (Vf) modified carbon paste electrode (Vf/CPE) for the determination of 4-aminophenol. Herein, a facile in-situ L-Valine film was developed by electrochemical polymerization method onto the surface of bare carbon paste electrode (BCPE) with the help of cyclic voltammetry (CV) technique. A two-folds of electrochemical peak current enhancement was achieved at Vf/CPE in comparison with BCPE towards the determination of 4-aminophenol in optimum pH 7.0 of phosphate buffer solution (PBS). This was achieved due to the large surface area and conductive nature of Vf/CPE, which was concluded through the techniques of cyclic voltammetry and electrochemical impedance spectroscopy (EIS). The effect of pH of buffer and scan rate studies were successfully studied. Morphological changes of BCPE and Vf/CPE was studied with the help of scanning electron microscopy (SEM). The formation of Vf on CPE was also analyzed by Fourier transform infrared (FTIR) spectra. Under the optimized conditions, the limit of detection (LOD) and limit of quantification (LOQ) values of 4-aminophenol were estimated with the aid of chronoamperometry (CA) technique and was found to be 9.8 μM and 32 μM, respectively. Finally the proposed method was found to have satisfactory repeatability, reproducibility and stability results with low relative standard deviation (RSD) values.

Polycaprolactone-enabled sealing and carbon composite electrode integration into electrochemical microfluidics

Combining electrochemistry with microfluidics is attractive for a wide array of applications including multiplexing, automation, and high-throughput screening. Electrochemical instrumentation also has the advantage of being low-cost and can enable high analyte sensitivity. For many electrochemical microfluidic applications, carbon electrodes are more desirable than noble metals because they are resistant to fouling, have high activity, and large electrochemical solvent windows. At present, fabrication of electrochemical microfluidic devices bearing integrated carbon electrodes remains a challenge. Here, a new system for integrating polycaprolactone (PCL) and carbon composite electrodes into microfluidics is presented. The PCL : carbon composites have excellent electrochemical activity towards a wide range of analytes as well as high electrical conductivity (∼1000 S m-1). The new system utilizes a laser cutter for fast, simple fabrication of microfluidics using PCL as a bonding layer. As a proof-of-concept application, oil-in-water and water-in-oil droplets are electrochemically analysed. Small-scale electrochemical organic synthesis for TEMPO mediated alcohol oxidation is also demonstrated.

Simultaneous detection of acetaminophen and 4-aminophenol with an electrochemical sensor based on silver–palladium bimetal nanoparticles and reduced graphene oxide

Simultaneous detection of acetaminophen and 4-aminophenol with a highly sensitive electrochemical sensor based on silver–palladium bimetal nanoparticles and reduced graphene oxide.

Efficient electrochemical determination of p-aminophenol using a novel tricomponent graphene-based nanocomposite

Design and synthesis of a gold nanoparticle@dithiooxamide functionalized graphene (AuNP@DFG) nanocomposite is reported herein, which is employed for the electrochemical determination of p-aminophenol successfully.

Label-Free Sensing in Microdroplet-Based Microfluidic Systems

Droplet microfluidic systems have evolved as fluidic platforms that use much less sample volume and provide high throughput for biochemical analysis compared to conventional microfluidic devices. The variety of droplet fluidic applications triggered several detection techniques to be applied for analysis of droplets. In this review, we focus on label-free droplet detection techniques that were adapted to various droplet microfluidic platforms. We provide a classification of most commonly used droplet platform technologies. Then we discuss the examples of various label-free droplet detection schemes implemented for these platforms. While providing the research landscape for label-free droplet detection methods, we aim to highlight the strengths and shortcomings of each droplet platform so that a more targeted approach can be taken by researchers when selecting a droplet platform and a detection scheme for any given application.

Facile synthesis of MnO2-embedded flower-like hierarchical porous carbon microspheres as an enhanced electrocatalyst for sensitive detection of caffeic acid

Tailored designs/fabrications of hierarchical porous advanced electrode materials are of great importance for developing high-performance electrochemical sensors. Herein, we demonstrate a simple and low-cost in situ chemical approach for the facile synthesis of MnO₂-embedded hierarchical porous carbon microspheres (MnO₂/CM). By the characterizations of scanning electron microscopy, X-ray photoelectron spectroscopy, X-ray powder diffraction and energy dispersive spectroscopy, we evidenced that the synthesized product were flower-like carbon microspheres (CM) assembled by the bent flakes with thickness of about several nanometers and MnO₂ nanorods were highly dispersed and successfully decorated on the CM layers, resulting in a rough surface and three-dimensional microstructure. The greatest benefit from the combined porous CM with MnO₂ nanorods is that the MnO₂/CM modified electrode has the synergetic catalysis effect on the electro-oxidation of caffeic acid, leading to the remarkable increase in the electron transfer rate and significant decrease in the over-potential for the caffeic acid oxidation in contrast to the bare electrode and CM modified electrode. This implies that the prepared MnO₂/CM can be employed as an enhanced electrocatalyst for the sensitive detection of caffeic acid. Under the optimum conditions, the anodic peak current of caffeic acid is linear with its concentration in the range of 0.01-15.00 μmol L^-1, and a detection limit of 2.7 nmol L^-1 is achieved based on S/N = 3. The developed sensor shows good selectivity, sensitivity, reproducibility, and also excellent recovery in the detections of real samples, revealing the promising practicality of the sensor for the caffeic acid detection.