Platform For Selective Detection Research Articles

Graphitic Carbon Nitride: A Novel Two-Dimensional Metal-Free Carbon-Based Polymer Material for Electrochemical Detection of Biomarkers

Graphitic carbon nitride (g-C3N4) has gained significant attention due to its unique physicochemical properties as a metal-free, two-dimensional, carbon-based polymeric fluorescent substance composed of tris-triazine-based patterns with a slight hydrogen content and a carbon-to-nitrogen ratio of 3:4. It forms layered structures like graphite and demonstrates exciting and unusual physicochemical properties, making g-C3N4 widely used in nanoelectronic devices, spin electronics, energy storage, thermal conductivity materials, and many others. The biomedical industry has greatly benefited from its excellent optical, electrical, and physicochemical characteristics, such as abundance on Earth, affordability, vast surface area, and fast synthesis. Notably, the heptazine phase of g-C3N4 displays stable electronic bands. Another significant quality of this semiconductor material is its excellent fluorescence property, which is also helpful in preparing biosensors. Based on g-C3N4, electrochemical biosensors have provided better biocompatibility, higher sensitivity, low detection limits, nontoxicity, excellent selectivity, and surface versatility of functionalization for the delicate identification of target analytes. This review covers the latest studies on using efflorescent graphitic carbon nitride to fabricate electrochemical biosensors for various biomarkers. Carbon nitrides have been reported to possess excellent electroactivity properties, a massive surface-to-volume ratio, and hydrogen-bonding functionality, thus allowing electrochemical-based, highly sensitive, and selective detection platforms for an entire array of analytes. Considering the preceding information, this review addresses the fundamentals and background of g-C3N4 and its numerous synthesis pathways. Furthermore, the importance of electrochemical sensing of diverse biomarkers is emphasized in this review article. It also discusses the current status of the challenges and future perspectives of graphitic carbon nitride-based electrochemical sensors, which open paths toward their practical application in aspects of clinical diagnostics.

Tailoring a novel all-in-one host-guest solid-state electrochemiluminescence platform for selective detection of spermine using cucurbit-[6]-uril modified [Ru(bpy)3]2+ electrode

Herein, a novel solid-state electrochemiluminescence (ECL) based on electrochemically incorporated [Ru(bpy)3]2+ on nafion modified glassy carbon electrode ([Ru(bpy)3]2+-Nafion/GCE) followed by chemisorption of cucurbit-[6]-uril (CB-[6]) on Ru(bpy)3]2+-Nafion/GCE (as CB-[6]-[Ru(bpy)3]2+-Nafion/GCE) has been developed for selective sensing of spermine (SPM) which belongs to the class of aliphatic biogenic amines and overexpression of SPM is associated with several cancers, particularly “Prostate Cancer” (PCa). Interestingly, the ECL emission of [Ru(bpy)3]2+ be enhanced significantly in the presence of CB-[6] modified [Ru(bpy)3]2+-Nafion/GCE. This is due to inherent ability of CB- [6] act as a co-reactant accelerator. Upon the addition of SPM, the ECL emission was further enhanced due to electron transfer reaction between SPM and [Ru(bpy)3]3+. Selectivity of the proposed ECL sensor towards SPM arises from the host-guest interaction between the CB-[6] and SPM, follows the anodic co-reactant ECL reaction (oxidative reduction mechanism) by confirmation of electrochemical and spectroscopic results like electron spin resonance (EPR) and ECL spectra. The proposed solid-state ECL sensor platform is selectively detect to SPM for a linear range of 10 nM - 5 mM with detection limit (LoD) of 1.4 nM at physiological pH conditions. In addition, the developed ECL platform of CB-[6]-[Ru(bpy)3]2+-Nafion/GCE has been successfully verified to the sensing of SPM in the urine sample, proving the practicability of the proposed sensor is suitable for clinical analysis.

Nanocomposite-modified nanopores: A promising platform for selective detection of copper ions

This research introduces an innovative platform designed for the selective detection of copper (II) (Cu2+) ions, employing a singular nanopore embedded within a 12 μ m-thick polyethylene terephthalate (PET) membrane. The track-etched nanopore was subsequently modified with nanomaterials in an allylamine hydrochloride (PAH)-modified asymmetric nanopore through electrostatic interactions. The nanomaterials included copper oxide (CuO), graphene oxide (GO), and their composite (GO/CuO), were synthesized using wet chemistry, and their structures and optical properties were thoroughly investigated using x-ray diffraction and diffuse reflectance spectroscopy. In the distinctive feature of the platform, Cu2+ ions gain access to coordination sites across a broad surface covered by the immobilized nanomaterials, facilitating effective binding. The selective response of GO/CuO modified pores towards Cu2+ ions was notably observed through ion transportation (I –V) studies, surpassing the response of unmodified nanopores and those modified with CuO alone. This selective behavior was demonstrated in the presence of various monovalent and divalent competing ions. Quantitative assessment of I –V studies was conducted by evaluating the intrinsic rectification ratio of asymmetric nanopores, providing a robust measure of platform's efficacy. Furthermore, we identified the optimal pH for detecting Cu2+ ions as 7, enhancing the specificity and accuracy of our method.

Electroactive ferrites nanostructure driven electrochemical platform for selective detection of dopamine

This study proposes a new electrochemical platform based on electroactive vanadium ferrites (VFe2O4) for the highly selective detection of dopamine (DA). VFe2O4 were synthesized with the sol–gel auto-ignition method and characterized by X-ray diffraction (XRD), Scanning electron microscopy (SEM), impedance analyzer, and cyclic voltammetry. The characterization study revealed that the VFe2O4 have a single-cubic structure with agglomerated structure. The VFe2O4 showed the multi-ions-based increment in the dielectric constant. The VFe2O4 sensor was fabricated by drop-casting method on a glassy carbon (VFe2O4-GCE) electrode with the addition of Nafion and applied for electrochemical detection of DA (a common neurotransmitter) in pharmaceutical preparations and biological samples. The results of electrochemical analysis of DA in the concentration range of 0.05 – 12.3 µM by using VFe2O4-GCE showed a linear response (co-efficient of determination R2 = 0.995) with the limit of detection and quantification (LOD/LOQ) as 0.0087 and 0.029 μM, respectively.

Fabrication of an electrochemical sensor based on molecular imprinting technology for detecting elemene

This paper presents the fabrication of an electrochemical sensor based on molecular imprinting technology for the detection of elemene, a bioactive compound with various pharmacological activities. The sensor was prepared by electrochemically polymerizing acrylamide and N,N-methylenebisacrylamide in the presence of dopamine hydrochloride and phytic acid as functional monomers, with elemene as the template molecule. The resulting molecularly imprinted polymer film on the glassy carbon electrode exhibited specific recognition sites for elemene. The sensor's electrochemical performance was systematically investigated using cyclic voltammetry and electrochemical impedance spectroscopy. The sensor showed excellent selectivity, sensitivity, stability, and reproducibility for elemene detection. The optimized sensor parameters, such as the number of polymerization cycles and elution time, were determined. The sensor exhibited a linear response to elemene in the concentration ranges of 10 μM to 0.1 mM and 50 nM to 10 μM, with a detection limit of 2.7 nM. The proposed electrochemical sensor offers a rapid, label-free, and selective detection platform for elemene, eliminating the need for complex sample preparation and expensive labeling reagents. It has the potential for application in quality control, safety assessment, and therapeutic efficacy evaluation of elemene-containing products.

Dye adsorbed few‐layer thick Ti3C2Tx‐MXenes for direct electrochemical detection of CD44 proteins

AbstractThe direct electrochemical detection of cancer biomarkers using single single‐component platforms is challenging. Herein, we propose constructing an efficient screen‐printed electrode (SPE) based platform for selective detection of CD44 proteins, a non‐kinase transmembrane glycoprotein. A sensing platform, MB‐MX/HA/SPE, was developed by incorporating few‐layered Ti3C2Tx nanosheets pre‐loaded with methylene blue (MB) dye. The nanosheets were subsequently immobilized with hyaluronic acid (HA), which served as a ligand for the specific recognition of CD44. The simple electrode configuration and the highly conductive Ti3C2Tx facilitated the electrochemical oxidation of MB, generating a reference SWV signal that declined proportionally with the increasing concentration of CD44 owing to ligand (HA)‐protein interaction. The sensor could register a sensitive inhibition response in the concentration range of 0.1 to 7.25 ng.mL−1 with a detection limit of 1.2×10−2 ng.mL−1 for CD44 proteins. Moreover, the synergistic combination of the highly conductive/adsorptive Ti3C2Tx nanosheets and hyaluronic acid (HA) led to strong antifouling characteristics even in the presence of other common proteins, such as bovine serum albumin (BSA), haemoglobin (Ig), immunoglobulin G (IgG), prostate‐specific antigen (PSA), and neuron‐specific enolase (NSE). The proposed strategy eliminates the need for additional components in the electrode modification procedure. In addition, incorporating MXenes as electrode material paves the way for developing sensitive biosensors with prospective applications in cancer diagnosis.

A water-soluble small molecular fluorescent sensor based on phosphazene platform for selective detection of nitroaromatic compounds.

Nitro-aromatic compounds have a deleterious effect on the environment and they are extremely explosive. Therefore, societal concern about exposure to nitro-aromatic compounds encourages researchers to develop selective and sensitive detection platforms for nitro-aromatic compounds in recent years. In this paper, a new 100% water-soluble cyclotriphosphazene-based bridged naphthalene material (4) was prepared as a small molecule fluorescent sensor for ultra-selective detection of nitro-aromatic compounds. The chemical structure of 4 was extensively characterized by mass spectrometry and nuclear magnetic resonance spectroscopies (31P, 13C, 1H). The photo-physical properties of the newly developed sensing system were investigated by steady-state fluorescence and UV-Vis absorption spectroscopies. The fluorescence sensor behaviors were extensively evaluated after treatment with the most commonly used metal cations, anions, competitive aromatic compounds, saccharides, and organic acids. The developed fluorescent sensing system (4) demonstrated ultra-selective fluorescence "turn-off" signal change toward nitro-aromatic compounds while other tested competitive species caused negligible changes. To evaluate selectivity, time-resolved, steady-state 3D-fluorescence and UV-Vis absorption spectroscopies were used in fully aqueous media. Moreover, theoretical calculations (density functional theory and time-dependent density functional theory) were applied and discussed to identify fluorescence sensing mechanisms toward nitroaromatic compounds for the presented sensing system.

A novel “signal-off” photoelectrochemical sensing platform for selective detection of rutin based on Cu2SnS3/TiO2 heterojunction

In this study, a novel and ultrasensitive photoelectrochemical (PEC) sensor was developed for highly selective detection of rutin with a “signal-off” pattern based on Cu2SnS3-modified TiO2 nanotube arrays (NTAs) under UV light irradiation. Herein, the highly ordered TiO2 nanotube arrays were grown on the surface of Ti foil using an anodization process, and then Cu2SnS3 nanoparticles (NPs) were deposited on TiO2 NTAs by electrodeposition method. It was found that the Cu2SnS3/TiO2 NTAs/Ti electrode exhibited a much-increased photocurrent response compared to the bare TiO2 NTAs/Ti electrode owing to the synergistic effect between Cu2SnS3 nanoparticles and TiO2 NTAs, which could accelerate the separation of electron-hole pairs. In the presence of rutin,the PEC response was reduced due to the steric hindrance effect caused by the interaction between Cu2SnS3 nanoparticles and rutin. Under optimum conditions, the fabricated PEC sensor indicated a widespread linear range of 0.001 nM–100 µM toward rutin with an extremely low detection limit (LOD) of 0.0007 nM. Moreover, the experimental results revealed that the proposed PEC sensor possessed good stability, favorable selectivity, outstanding repeatability, and reproducibility. Meanwhile, the proposed PEC sensor was successfully used to determine rutin content in real samples, and satisfactoryresults were obtained.

A novel "turn-off" photoelectrochemical aptasensing platform for selective detection of tobramycin based on the Ti3C2-MoS2/BiOI heterojunction.

Tobramycin (TOB), as a widely used antibiotic, poses severe unpredictable risks to ecology and health. In this study, a novel photoelectrochemical (PEC) adapter sensor, based on its "turn-off" PEC mode, was constructed for TOB detection. This visible-light-driven photoelectrochemical (PEC) aptasensor was successfully developed for TOB detection using Ti3C2-MoS2/BiOI and TOB aptamer probes. When TOB was captured by probes anchored on the modified electrode, a decreased photocurrent was also noted due to steric hindrance and this further hindered electron transfer. Under optimal conditions, 0.001 ng mL-1 to 40 ng mL-1 of TOB could be identified, with the detection limit being as low as 0.5 pg mL-1. At the same time, actual samples were also explored. Finally, the proposed sensor exhibited high specificity, satisfactory detectability and great reproducibility, thereby providing a novel approach for the detection of pollutants.

A coordination-driven fluorescent platform for selective detection of valine in living cells and food samples based on dopamine-functionalized nitrogen doped graphene quantum dots and its construction of molecular logic gate

The design of a fluorescent system for tracking valine remains a challenge till date. This work demonstrated the first use of the metal complex of dopamine-functionalized nitrogen doped graphene quantum dots (N-GQDs-DA) as coordination-driven fluorescent platform for selective detection of valine in human serum and real food samples. The fluorescence of the N-GQDs-DA was quenched after the addition of Cr3+, which acts as both a fluorescence quencher and a receptor for target molecule. The quenched fluorescence of the N-GQDs-DA/Cr3+ sensing system was linearly restored as the valine concentration increased from 1.33 × 10−4 M to 62.5 × 10−4 M. Different coordination states of Cr3+ opened or blocked a PET course, which constructed “turn-off or turn-on” fluorescence switching. The “INHIBIT” logic gate operation can be carried out using the Cr3+ and valine as inputs and the emission bands EM 315 nm and EM 440 nm as outputs, indicating that they have promising applications in intelligent dual analyte sensing systems. MALDI-TOF mass spectra elucidated the formation of a low-fluorescent species [C55H32Cl3Cr2N4O10]+ and a high-fluorescent species [C70H58Cr2N7O14]+ without and with valine, respectively. This methodology provides a new concept for the design and development of highly selective optical system for single amino acid.

Rapid Selective Detection of Ascorbic Acid Using Graphene-Based Microfluidic Platform

In this paper, we present a compact microfluidic platform for selective detection of ascorbic acid. The microfluidic chip was fabricated by xurography technique with microfluidic channel placed between the silver electrodes. To increase the conductivity of the platform and enhance electron transfer process, a graphene sheet was deposited in the gap between the electrodes. The suspension of tablets with ascorbic acid and a mixture of ascorbic acid and isomalt, a sugar substitute, were injected in the microfluidic channel. Measuring electrical parameters at the silver contacts, it was possible to successfully differentiate ascorbic acid from isomalt. The sensing mechanism of the developed microfluidic platform is based on the increase of the overall conductivity with the increase of the concentration of ascorbic acid, resulting in the decrease of the resistive parameters and increase of the capacitive parameters of the proposed equivalent electrical circuit. The addition of graphene was found to improve the response linearity by 5.28% and lower the limit of detection and quantification by 12%, compared to the reference structure without graphene.

Electronic nose system based on a functionalized capacitive micromachined ultrasonic transducer (CMUT) array for selective detection of plant volatiles

Here, a small, low-power, wireless gas sensor platform for selective detection of volatile organic compounds (VOCs) released from plants under different abiotic or biotic stress conditions is described. This sensor platform is implemented based on a capacitive micromachined ultrasonic transducer (CMUT) array, in which elements were functionalized with a variety of materials including polymers, phthalocyanines, and metals to improve selectivity. Input impedance measurements of the functionalized CMUT array were compared to pre-coating measurements to analyze the mechanical loading. The CMUT arrays were then exposed to VOCs known to be emitted by plants with different concentrations under dry air flow at room temperature. The results demonstrated that 1-Octanol created the strongest response across different channels and a resolution of 3-ppb was calculated for the CMUT element functionalized using silver ink when exposed to 1-Octanol. The relative responses of different channels to tested volatiles were observed to be different. The k-nearest neighbor (k-NN) algorithm was used for the gas classification by dividing the data to training and test groups. The k-NN results showed that the gases at low concentrations were successfully classified with better than 97 % accuracy. Finally, to emulate the ambient atmosphere for plants, the gas tests were repeated by adding different levels of humidity to the gas flow. With a minimum 98 % accuracy, the k-NN classifier demonstrated that the functionalized CMUT array can be used for selective detection of the group of plant VOCs used in this study, even at different relative humidity levels in the ambient atmosphere.

Highly stable Cd(II)-MOFs based on 2,6-naphthanlenedisulfonate and bisimidazole ligands: A new platform for selective detection of Cu2+ and efficient removal of iodine

Two new metal-organic frameworks (MOFs) namely, [Cd (nds) (bimh)2·(bimh)]n (1) and [Cd (nds) (bimb)2]n (2), (nds ​= ​2,6-naphthalenedisulfonate; bimh ​= ​1,6-bis-(imidazole-1-yl)-hexane; bimb ​= ​1,1'-(1,4-butanediyl)bis(imidazole)), have been hydrothermally synthesized. These complexes were characterized by IR spectroscopy, elemental analysis and X-ray single-crystal diffraction. Complex 1 possesses a 3D framework with 6-connected (412.63) pcu topology. Complex 2 shows a 2D layer with Schläfli symbol of (36) (46) (53). The adjacent layers are stacked offset with respect to each other, in an ABAB fashion. Both complexes 1 and 2 exhibit low detection limit and high selectivity toward Cu2+ through the luminescent quenching experiments. Further, the adsorption experiments indicate that complex 1 could efficiently remove I2 from the cyclohexane solution after 20 ​h with an adsorption capacity of 148.5 ​mg/g.

Carbon quantum dots: Comprehensively understanding of the internal quenching mechanism and application for catechol detection

Abstract Carbon quantum dots (CQDs), a new member of the nanocarbon family, are emerging as attractive optical sensing material. At present, there is still a lack of in-depth investigation on internal responsive mechanism of CQDs as their fluorescence is quenched by analytes. In this work, ethylenediamine (EDA) functionalized carbon quantum dots (N-CQDs) are synthesized through the protection/deprotection of one amine group and the amidation reaction on CQDs surface. According to the fluorescence response of N-CQDs in catechol (CTC) solution and under different environmental conditions, it is found that the EDA on the surface of N-CQDs could spontaneously combine with CTC via Michael addition or Schiff base reaction to form static compounds, which serve as electron donor to effectively quench the fluorescence originated from sp2 carbogenic core area and “surface state” of N-CQDs, but have little impact on the emission from “edge state” of N-CQDs. This is the first time that the “inertness” of “edge state” was observed. Based on the comprehensive analysis of quenching mechanism, the excitation wavelength (λex=310nm) corresponding to the “core state” of N-CQDs was selected, and a simple, highly sensitive and selective detection platform for CTC quantification is established.

Aptamer-functionalised magnetic particles for highly selective detection of urinary albumin in clinical samples of diabetic nephropathy and other kidney tract disease

We report a new highly selective detection platform for human albumin (HA) in urine based on aptamer-functionalised magnetic particles. Magnetic separation and re-dispersion was utilised to expose the HA-bound particles to a methylene blue solution. A second magnetic collection step was then used to allow the methylene blue supernatant to be reduced at an unmodified screen-printed electrode. Since methylene blue adsorbs to HA, the reduction current fell in proportion to HA concentration. There was no interference from compounds such as dopamine, epinephrine, vanillylmandelic acid, normetanephrine, metanephrine and creatinine in artificial urine at the concentrations at which they would be expected to appear. A calibration equation was derived to allow for the effect of pH on the response. This enabled measurement to be made directly in clinical urine samples of varying pH. After optimisation of experimental parameters, the total assay time was 40 min and the limit of detection was between 0.93 and 1.16 μg mL−1, depending on the pH used. HA could be detected up to 400 μg mL−1, covering the range from normoalbuminuria to macroalbuminuria. Analysis of urine samples of patients, with diabatic nephropathy, type I & II diabetes mellitus and chronic kidney disease, from a local hospital showed good agreement with the standard urinary human albumin detection method.

Highly-sensitive and fast detection of human telomeric G-Quadruplex DNA based on a hemin-conjugated fluorescent metal-organic framework platform

The formation of G-quadruplex (G4) structures in Human telomeric DNA (H-Telo) has been demonstrated to inhibit the activity of telomerase enzyme that is associated with the proliferation of many cancer cells. Accordingly, G-quadruplex structures have become one of the well-established targets in anticancer therapeutic strategies. And, the development of simple and selective detection platforms for G4 structures has become a significant focus of research in recent years. In this study, a simple “off-on” fluorometric method was developed for the selective detection of picomolar quantities of H-Telo G4 DNA based on a fluorescent cerium-based metal organic framework (Ce-MOF) conjugated with hemin to form the sensing probe, Hemin@Ce-MOF. The solvothermal synthesis of the Ce-MOF took advantage of 5-aminoisophtlalic acid (5AIPA) as the organic bridging ligand, (Ce2(5AIPA)3(DMF)2). Characterization of Ce-MOF and Hemin@Ce-MOF was performed by XRD, XPS, TEM, SEM, BET and FTIR techniques. The detection and quantification of the H-Telo was carried out through the adsorption/incorporation of hemin molecules on the pores and surface of Ce-MOF resulting in the fluorescent quenching of the system followed by the restoration of the fluorescence upon addition of H-Telo probably due to a competition between H-Telo and Ce-MOF to bind to hemin. The impact of the key variables including MOF quantity, hemin concentration and detection time was investigated and optimized. Under the optimized conditions, the developed probe provides a limit of detection (LOD) of 665 pM, linear dynamic range (LDR) of 1.6–39.7 nM and excellent selectivity towards H-Telo. Taken together, these results present a simple, novel and superior platform for the selective detection of H-Telo G4 DNA.

Construction of 3D Bi/ZnSnO3 hollow microspheres for label-free highly selective photoelectrochemical recognition of norepinephrine.

Herein, we reported a label-free and reliable photoelectrochemical (PEC) platform for highly selective monitoring of norepinephrine (NE) based on metallic Bi nanoparticles anchored on hollow porous ZnSnO3 microspheres (3D Bi/ZnSnO3) via a simple solvothermal strategy. The designed 3D Bi/ZnSnO3 Schottky junction exhibited a unique photoanodic response toward NE among other catechol derivatives, such as epinephrine (EP) and dopamine (DA), and effectively shielded the interference from thirteen coexisting biomolecules like uric acid (UA) and ascorbic acid (AA). High selectivity and excellent sensitivity could be correlated to the unique chelating coordination interaction between NE and Zn2+ at surface sites as well as the efficient carrier separation of Bi/ZnSnO3, thereby developing a novel "signal-on" label-free and selective strategy for NE detection. The proposed Bi/ZnSnO3-based PEC sensor achieved remarkable NE biosensing with a low detection limit of 0.68 nmol L-1 and a wide response ranging from 0.002 to 350.0 μmol L-1. The applicability of this biosensor was realized for the selective analysis of NE in human serum, human urine and injection samples, laying the foundation for the label-free PEC monitoring of NE in biological fluids.

One-step synthesis of levodopa functionalized carbon quantum dots for selective detection of tyrosinase and inhibitor screening

Tyrosinase (TYR), a key enzyme for melanin biosynthesis, is an important biomarker for melanoma, thus a biosensor that can specifically detect and image tyrosinase would be in urgent demand to diagnose tyrosinase related disease. Therefore, a novel levodopa (L-Dopa) functionalized carbon quantum dots (Dopa-CQDs) was firstly constructed and synthesized by a convenient “one-step synthesis” strategy without any modified steps, utilizing L-Dopa and urea as precursors. The Dopa-CQDs also illustrated excellent linear relationship with a wide range (0–1200 U·L−1) and a low detection limit of 7.3 U·L−1. Importantly, the nanosensor exhibited high selectivity for tyrosinase over other biological substances including various amino acids and intercellular proteases. Moreover, the Dopa-CQDs demonstrated practicability for TYR detection in human serum samples and inhibitor screening with satisfactory results. Particularly, the designed biosensor was successfully applied for intracellular TYR detection with excellent biocompatibility and cellular imaging capability, which provided a novel platform for selective detection of tyrosinase in biosystems. The novel methodology can be extended for fabricating novel biosensor for other analytes in various field, which will illustrate great importance for both fundamental research in biological systems and potential practical applications in clinical diagnosis.

Surface molecularly-imprinted magnetic nanoparticles coupled with SERS sensing platform for selective detection of malachite green

Herein, a novel analytical method was reported for sensitive and selective quantification of malachite green (MG) in tap water and carp samples based on a combination of surface-enhanced Raman spectroscopy (SERS) and molecular imprinting technology. For this purpose, surface molecularly-imprinted magnetic nanoparticles (MIP@Fe3O4 NPs) were synthesized through recently developed living/controlled radical polymerization mechanism referred to as reversible chain transfer catalyzed polymerization (RTCP). Surface characterization of MIP@Fe3O4 NPs was carried out in detail by using the combination of several analytical techniques and the results showed the presence of a thin polymer layer on the nanoparticles. Rebinding properties, selectivity and reusability of the nanoparticles were investigated and the obtained results indicated the prepared nanoparticles had excellent selectivity, high adsorption capacity, fast adsorption kinetics and multiple-uses with an imprinting factor of 3.86. Then, silver dendrites (Ag NPs) were deposited on silicon wafers and used as SERS sensing platform. Moreover, surface properties of the SERS substrate were also investigated in detail in terms of stability, reusability and homogeneity. After that, the eluted MG from the imprinted nanoparticles was dropped on the sensing platform and SERS analysis was carried out. Under optimized conditions, limit of detection and limit of quantification were determined to be 1.50 pM and 4.96 pM for tap water, respectively and 1.62 pM and 5.38 pM for carp samples, respectively within acceptable recovery rates and standard deviations. The overall results indicated that the proposed method can be effectively used for the quantification of trace amounts of MG in tap water and carp samples. Moreover, the proposed method is promising for development of new ways to prepare MIPs via surface-initiated RTCP.

A metal-enhanced fluorescence sensing platform for selective detection of picric acid in aqueous medium

Apart from national security and military purposes, it is also of great importance to detect picric acid (PA) in aqueous solution for pollution control. Herein, we report a gold nanoparticle (AuNP)-based sensor for detection of PA in aqueous condition, based on metal-enhanced fluorescence (MEF) of poly(allylamine)hydrochloride (PAH). Notable enhancement in fluorescence intensity is observed when PAH is incubated with Au@SiO2 nanoparticles, where silica shell controls the distance between gold core and PAH. Almost ∼280 fold enhancement is recorded when PAH is incubated with ∼45 nm diameter Au nanoparticles. A significant reduction in excited state lifetime followed the enhancement in fluorescence intensity, identifying the mechanism to be primarily obtained from the intrinsic radiative decay rate enhancement of PAH. The MEF sensor shows excellent selectivity for detection of PA in water, among similar electron deficient compounds via fluorescence quenching. The detection limit of the sensor is calculated to be 79 nM, in the linear range. Detection of PA is demonstrated in simulated water samples, where matrix effects are taken into account to assess the efficacy of the sensor.