Nanomolar Level Detection Research Articles

A rhodamine based nanosensor platform for Hg2+ sensing in near–perfect aqueous medium: Smartphone, test strip and real sample applications

Herein, a rhodamine based nanosensor platform (RHD–NPs) was designed and prepared for the sensing of Hg2+ in the near–perfect aqueous medium (v/v, 0.01/99.99, acetone/water). The structure, aqueous stability, surface charge and particle size of RHD–NPs were analyzed by using zeta particle sizer, scanning electron microscopy (SEM) and UV–Vis spectrophotometry. The spherical shaped morphology ofRHD–NPshas 61.4 nm particule size. The interaction ability of RHD–NPstowards various heavy metal ions was evaluated with UV–Vis and fluorescence spectroscopies. After the transferring of Hg2+ to RHD–NPs, a new absorption band at 562 nm was observed due to the ring–opening mechanism of rhodamine structure. The remarkable emission enhancement at 582 nm was observed through the adding of Hg2+ because of chelation–enhanced fluorescence (CHEF) and aggregation–induced enhanced emission (AIEE) phenomena. RHD–NPs nanosensor system showed good selectivity for Hg2+ monitoring with a nanomolar–level detection limit of 6.56 nM. The binding constant ofRHD–NPswith Hg2+ was determined to be 10.06 × 103 M−1 based on the Benesi–Hildebrand graph and a maximum value of Job’s graph was about 0.5 ratio (1:1) between RHD–NPs and Hg2+.The smartphone–based technique revealed an outstanding potential of the RHD–NPsplatform for the sensing of Hg2+ without further device. A visual colorimetric strip based on papers with excellent selectivity towards Hg2+ without interfering competition ions, was produced with the white–to–pink color signal change. The RHD–NPswas also employed for the quantitative determination and real–time monitoring of Hg2+ in real samples.

Light responsive, electrochemically dimerizable, capture and release device based on photochromic oxazine for nanomolar level detection of Hg2+ ions

Photochromic oxazine was synthesized and screened for the colorimetric detection of heavy metal ions in an aqueous solution. The “OX” (closed) form of the oxazine converted rapidly to the “IN” (open) form in presence of mercuric ions. The mercuric ion-induced structural alteration led to the appearance of an intense band in the visible region of the absorption spectrum in an aqueous acetonitrile medium. Naked eye, UV–Visible, cyclic voltammetry (CV), and smartphone-based techniques were successfully employed to study the detection process. The probe provided a 40 nM limit of detection value for Hg2+ ions using CV. The 1H NMR spectroscopy confirmed the interaction of the mercury ion with the oxazine unit and the ring-opening process. The cyclic voltammetric studies indicated the formation of CC bonds producing dimeric oxazine. The process of formation of a CC bond was investigated in the presence of Hg2+ ions, which was used as a detection method. The development of color in the complex was exploited to develop the solution and paper-based detection techniques aided by digital images of easily available smartphones and software. The probe-Hg2+ complex released mercuric ion upon exposure to visible light (450 nm) in water.

Temperature abetted synthesis of novel magnesium stannate nanoparticles assisted for nanomolar level detection of hazardous flavonoid in biological samples

Fabrication of temperature-influenced nanoparticles over the superficial region of glassy carbon electrode (GCE) stimulates the electrocatalytic activity owing to their morphology, defective sites, and higher active surface area, etc. In this regard, we have fabricated annealed magnesium stannate nanoparticles (Mg2SnO4 NPs) on GCE for nanomolar level detection of hazardous flavoring and pharmaceutical compound Rutin (RT). To analyze the impact of temperature, we have compared annealed Mg2SnO4 NPs with unannealed magnesium stannate hydrate (MgSnO3·3H2O) particles. The physicochemical properties of synthesized materials were characterized with different microscopic and spectroscopic techniques. From these studies, annealed Mg2SnO4 NPs formed purely without any flith and existence of water molecules as compared to unannealed MgSnO3·3H2O. Moreover as fabricated, Mg2SnO4 NPs/GCE outcomes with higher redox behavior compared to other electrodes in presence of RT at optimized working buffer (pH = 7.0). Interestingly, the electrode successfully established a dual wider linear response (0.062–34.8 & 34.8–346.8 µM) with a nanomolar detection limit (1 nM) and higher sensitivity. The practicability analysis of the proposed sensor also affords excellent selectivity, reproducibility, repeatability, reversibility, and storage stability. Furthermore, the real sample analysis was carried out in blood and orange samples fallout with better recovery results.

Ultrafast and nanomolar level detection of H2S in aqueous medium using a functionalized UiO-66 metal–organic framework based fluorescent chemosensor

A new robust Zr(iv) based UiO-66 MOF with 4-nitrophenyl functionalization was used for the rapid, selective and nanomolar level fluorescence turn-on detection of H2S in the aqueous medium.

Nanomolar level detection of metal ions by improving the monodispersity and stability of nitrogen-doped graphene quantum dots

Highly fluorescent and stable nitrogen-doped graphene quantum dots used as nanosensor for the selective and sensitive detection of Fe3+ ions at nanomolar range based on the dynamic quenching.

Preparation of a portable calorimetry kit and one-step spectrophotometric nanomolar level detection of l-Histidine in serum and urine samples using sebacic acid capped silver nanoparticles

Abstract This work describes the synthesis of sebacic acid capped silver nanoparticles (SA-AgNPs) by the wet chemical method for the detection of l -Histidine in blood serum and urine samples. The synthesized SA-AgNPs were characterized by several techniques. The obtained particles were spherical in shape and the average diameter was calculated by HR-TEM images to be 11 nm. Moreover, the synthesized SA-AgNPs were stable for more than 3 months in solution. The synthesized SA-AgNPs showed the surface plasmon resonance (SPR) band at 420 nm. Interestingly, after the addition of 18.1 μM of l -Histidine into the SA-AgNPs solution, the SPR band absorbance decreased and the colour of the solution changed from brown to colourless. Based on the changes in the SPR band, we calculated the lowest detection limit to be 122 nM. The observed colour shift and spectral changes were due to the aggregation of SA-AgNPs induced by l -Histidine via hydrogen bonding interaction. Additionally, a possible mechanism is discussed. Furthermore, a 268-fold excess of common interferences did not interfere with the detection of 18.1 μM of l -Histidine. We successfully applied the SA-AgNPs probe for the detection of l -Histidine in blood serum and urine samples. Further, we validated our system with the HPLC technique. Importantly, we prepared a portable smartphone aided paper-based kit for on-site monitoring of l -Histidine. We strongly hope that this facile synthesis of SA-AgNPs and the portable paper-based kit will represent a step forward in the field of biosensing and materials science.

Nanomolar level detection of non-steroidal antiandrogen drug flutamide based on ZnMn2O4 nanoparticles decorated porous reduced graphene oxide nanocomposite electrode

Flutamide is a non-steroidal antiandrogen drug and widely used in the treatment of prostatic carcinoma. Nevertheless, the excessive intake and improper disposal could affect the living organisms. In this work, we have synthesized a new nanocomposite based on ZnMn2O4 nanoparticles and porous reduced graphene oxide nanosheets (ZnMn2O4-PGO) for the electrocatalytic detection of flutamide (FLU) drug. The crystallinity and morphological properties of ZnMn2O4-PGO composite examined by different characterization techniques such as X-ray diffraction, Raman spectroscopy and so on. The fabricated ZnMn2O4-PGO nanocomposite modified electrode exhibited superior electrocatalytic performance to FLU drug in an optimized pH electrolyte. Fascinatingly, the electrode received a wide linear range (0.05–3.5 µM) with limit of detection of 8 nM. Besides, the developed ZnMn2O4-PGO nanocomposite electrode showed good sensitivity 1.05 µAµM−1 cm−2 and excellent selectivity for FLU detection in presence of various interfering species. A developed disposable electrode was scrutinized to determine FLU level in human urine samples by spiking method and the results achieved good recoveries in real sample analysis.

A MC-spiropyran for smartphone assisted reversible, selective and nanomolar level detection of formic acid in water and gas phase

ABSTRACT A p-toluenesulfonate salt of benzothiazonium (merocyanine) dye substituted with diethylamine was synthesized to act as an optical probe. The probe was characterized using FT-IR, NMR, HR-MS and examined for a response towards polar molecular and ionic species using UV-Visible, fluorescence spectroscopic techniques. The probe displayed remarkable formic acid-responsive optical and aggregation properties in distilled water and at pH 7.6 (1.0 mM HEPES). The change in color was also exploited for smartphone assisted digital colorimetric analysis of formic acid and formate ions. The formic acid response can be switched off thermally. The emission response of the probe appeared in the visible region. The receptor can also be used to detect the vapors of formic acid reversibly in air. The computational calculations based on M06-2X/6-31+G(d), M06-2X/6-31+G(d,p) and CAM-B3LYP/6-31+G(d,p) methods were performed to investigate the complex formation at a molecular level. The time-dependent CAM-B3LYP/6-31+G(d,p) method-based calculations were also implemented to study the observed absorption spectra of the complex.

Novel 2‐hydroxynaphthalene‐based fluorescent turn‐on sensor for highly sensitive and selective detection of Al3+ and its application in imaging in vitro and in vivo

Excessive aluminum exposure in the human body has been held responsible for multiple adverse effects, and existing data underscore the significance of aluminum detection in environmental and biological systems. Developing high‐performance Al3+ fluorescent chemosensors can revolutionize our understanding of the physiological and pathological processes of Al3+ ions. Herein, we reported a highly sensitive and selective Schiff base fluorescence sensor, bis‐NAPPD (1,1'‐((1E,1'E)‐(pyridine‐2,3‐diylbis(azanylylidene))bis(methanylylidene))bis(naphthalen‐2‐ol)), which can recognize Al3+ ions and exhibits a remarkable turn‐on dual emission response (by ~23 fold) with a low nanomolar level detection limit (1.67 × 10−8 M) in methanol. Furthermore, the binding behavior and the turn‐on fluorescence probing mechanism of bis‐NAPPD were illustrated in detail by UV–vis titration, 1H NMR, and ESI‐MS spectroscopy as well as density functional theory calculations. Notably, bis‐NAPPD showed great potential for tracing Al3+ distribution in cells and living zebrafish larvae, and can also be applied in the fluorimetric detection of aluminum in sucralfate tablets with good precision and satisfactory accuracy, which may represent a promising Al3+ probe in bioimaging and biomedical applications.

Layered nanocomposite of zinc sulfide covered reduced graphene oxide and their implications for electrocatalytic applications.

Herein, we have synthesized zinc sulfide nanospheres (ZnS NPs) encapsulated on reduced graphene oxide (RGO) hybrid by an ultrasonic bath (50kHz/60W). The physical and structural properties of ZnS NPs@RGO hybrid were analyzed by TEM, XRD, EIS and EDS. As-prepared ZnS NPs@RGO hybrid was applied towards the electrochemical determination of caffeic acid (CA) in various food samples. The ZnS NPs@RGO hybrid modified electrode (GCE) exhibited an excellent electrocatalytic performance towards caffeic acid detection and determination, when compared to other modified electrodes. Therefore, the electrochemical sensing performance of the fabricated and nanocomposite modified electrode was significantly improved owing to the synergistic effect of ZnS NPs and RGO catalyst. Furthermore, the hybrid materials provide highly active electro-sites as well as rapid electron transport pathways. The proposed electrochemical caffeic acid sensor produces a wide linear range of 0.015-671.7µM with a nanomolar level detection limit (3.29nM). In addition, the real sample analysis of the proposed sensor has applied to the determination of caffeic acid in various food samples.

A Pentapeptide with Tyrosine Moiety as Fluorescent Chemosensor for Selective Nanomolar-Level Detection of Copper(II) Ions.

Herein, we have investigated principally with the use of UV and fluorescence (steady-state and time-resolved) spectroscopy the interactions between selected pentapeptides with tyrosine residue (EYHHQ, EHYHQ, EHHQY, and KYHHE) and various metal ions (Cu2+, Mn2+, Co2+, Ni2+, Zn2+, Cr3+, Cd2+, Ag+, Pb2+, Sr2+, Ba2+, Ca2+, Mg2+, Al3+, Fe2+, and Ga3+) in order to establish the relationship between the position of a tyrosine residue in the peptide sequence and the metal ion-binding properties. Among the peptides studied, EHYHQ was evaluated as an efficient and selective ligand for developing a chemosensor for the detection of copper(II) ions. While significant fluorescence emission quenching was observed for that peptide in the presence of Cu2+ cations, other metal cations used at the same and at considerably higher concentrations caused a negligible change of the fluorescence emission spectrum, indicating a high selectivity of EHYHQ for Cu2+ ions. Under optimum conditions, fluorescence intensity was inversely proportional to the concentration of Cu2+ ions. The limit of detection of Cu2+ ions with the use of EHYHQ was determined at the level of 26.6 nM. The binding stoichiometry of the complexes of the studied peptides with Cu2+ ions was evaluated spectrophotometrically and fluorimetrically (as in the case of EHYHQ confirmed by mass spectrometry) and found to be 1:2 (Cu2+-peptide) for all the investigated systems. Furthermore, the stability constant (K) values of these complexes were determined. The reversibility of the proposed Cu2+ ions sensor was confirmed, the pH range where the sensor acts was determined, while its analytical performance was compared with some other reported recently fluorescent sensors. The mechanism of the interactions between EHYHQ and Cu2+ was proposed on the basis of NMR spectroscopy investigations.

An ESIPT blocked highly ICT based molecular probe to sense Zn (II) ion through turn on optical response: Experimental and theoretical studies

A simple and low cost optical sensor (L) is synthesized by the condensation reaction and characterized systematically. Among the various tested metal ions, L selectively interacts with Zn2+ ion by inducing a 17-fold high fluorescence intensity with a 60 nm blue shift of emission maxima, changing colorless solution to intense yellow solution in 20 % aqueous acetonitrile. A mechanism for selective turn on optical response of L for Zn2+ was studied using UV–vis absorption and Fluorescence emission and is correlated with theoretical results. We propose that, a dual mechanism (ESIPT/ICT) is responsible for selective sensing of Zn2+ in 20 % aqueous acetonitrile. The Job’s plot, B-H plots and ESI-MS studies confirm the 1:1 stoichiometry between host-guest interaction. A reversible optical probe with nanomolar level detection limit is non-toxic and it could render pH dependent fluorescence measurements in a live physiological environment. The practical application of L for Zn2+ was explored through bio-imaging experiment in HeLa cells.

Nano-molar level detection of calcium folinate and methotrexate using a cationic surfactant and multivariate optimization: A simple tool for simultaneous and sensitive analysis

This study is the first report for simultaneous determination of calcium folinate (CF) and methotrexate (MTX) in nano-molar level using a simple modified carbon paste electrode (CPE) by cationic surfactants. N-dodecylpyridinium chloride (DPC) as a cationic surfactant has not yet been used successfully as a modifier in any simultaneous electrochemical measurements. Initially, the performance of DPC for modification of the electrode surface is compared with a well-known cationic surfactant. Then, after revealing the superiority of DPC, it is used as a modifier. Under the optimum conditions, using multivariate optimization, the oxidation peak current of CF in the presence of 10.0 µM MTX is linear in the concentration range of 0.1–10.0 µM with a detection limit of 17.5 nM. Under similar conditions, the oxidation peak current of MTX in the presence of 10.0 µM CF is linear in the concentration range of 0.05–10.0 µM with a detection limit of 9.3 nM.

Controllable and reversible proton transfer for inorganic cyanide visual sensing based on the deprotonation of azo-phenolic hydroxyl group

ABSTRACTMethods for optical detection of inorganic cyanide based on the single molecule sensor with high selectivity and sensitivity have attracted increasing interest recently due to the high toxicity of cyanide ions. In this work, a visual sensor (S1) containing both imidazole NH and azo-phenolic OH was synthesised and characterised. The spectral experimental data indicated that protic aqueous solution facilitated enhancing the selectivity of cyanide ions with the nanomolar-level detection limit in semi-aqueous solution. The visual sensing mechanism arising from the deprotonation of azo-phenolic OH and the enhancement of intramolecular charge transfer could be clearly demonstrated by titration experiments of 1H NMR, HR MS and energy changes between the HOMO−LUMO band gaps. Furthermore, the reversibility and reusability of S1 upon alternating addition of CN− and H+ were studied.

Dihydroxy-Substituted Coumarins as Fluorescent Probes for Nanomolar-Level Detection of the 4-Amino-TEMPO Spin Label.

This paper reports on dihydroxycoumarins as fluorescent probes suitable for the detection and determination of the nitroxide radical, namely 4-amino-TEMPO. Since 4-amino-TEMPO is used as a spin label for the detection of various radicals and damage caused by these species, its determination under physiological conditions might help us to understand the mechanism of the oxidative stress. Among different coumarins studied, only dihydroxy-substituted derivatives show high sensitivity, specificity, and selectivity for the nitroxide radical. In this assay, dihydroxy-substituted coumarins under the action of 4-amino-TEMPO show a very fast and significant increase in fluorescence intensity and lifetime. Among them 6,7-dihydroxycoumarin (esculetin) exhibits the strongest fluorescence enhancement (up to 40 times), with an estimated limit of detection equal to 16.7 nM—a significantly lower value when compared with UV-Vis or electron paramagnetic resonance (EPR) spectroscopy. The method is characterized by an easy procedure of sample preparation and very short time of analysis. The mechanism of the interaction between 6,7-dihydroxycoumarin and 4-amino-TEMPO has been examined with the use of a series of complementary techniques, such as steady-state and time-resolved fluorescence spectroscopy, UV-Vis spectroscopy, electron paramagnetic resonance spectroscopy, potentiometric titration, and high-performance liquid chromatography. It has been proven that the only route of the reaction in the system studied is a proton transfer from the molecule of esculetin to the amino group of the nitroxide. Biological studies performed on prostate cancer cells, breast cancer cells, and normal skin fibroblasts revealed significant anticancer properties of 6,7-dihydroxycoumarin, which caused a considerable decrease in the viability and number of cancer cells, and affected their morphology, contrary to normal fibroblasts. Furthermore, the experiment performed on prostate cancer cells showed that fluorescence emission of esculetin is closely related to intracellular pH—the higher pH, the higher observed fluorescence intensity (in accordance with a chemical experiment). On the other hand, the studies performed in different pH levels revealed that when pH of the solution increases, the observed fluorescence intensity enhancement under the action of 4-amino-TEMPO decreases (better sensing properties of esculetin towards the nitroxide in lower pH).

Lowering the limit of detection of ion-selective membranes backside contacted with a film of poly(3-octylthiophene)

Nanometer-sized membranes (thickness of ca 200 nm) backside contacted with a film of poly(3-octylthiophene) (POT) are here interrogated by an electrochemical protocol based on the accumulation and stripping of the target ion aiming at lowering its limit of detection (i.e., in the sub-micromolar range). Thus, using a membrane based on silver ionophore IV (Sigma-Aldrich), which is one of the ionophores regularly used in ion-selective membranes presenting a large binding constant (log βAg–ionophore ≈ 12), it is possible to detect 5 nM concentration of silver with the established methodology. Importantly, this is a 1000-fold lower concentration of silver compared with the case in which the same membrane is subjected to traditional cyclic voltammetry. Essentially, the control of the oxidation state of the POT film by applying a constant potential during a certain period of time (i.e., Eapp = 0 V for 720 s) in the presence of silver ions in the sample solution (from 5 to 100 nM) allows for an enrichment of the selective membrane in silver ions. As a result, a subsequent anodic linear sweep potential generates a voltammetric peak for silver transfer across the membrane that comprises a well-defined wave for such very low concentrations of silver in high sodium ion concentration background solution (10 mM NaNO3). Detection of nanomolar levels of silver in different types of natural and environmental waters is herein demonstrated and the results are validated using inductively coupled plasma mass spectrometry.

Enzyme-free electrochemical detection of nanomolar levels of the organophosphorus pesticide paraoxon-ethyl by using a poly(N-isopropyl acrylamide)-chitosan microgel decorated with palladium nanoparticles.

A rapid voltammetric method is described for the determination of the organophosphorus pesticide paraoxon-ethyl (PEL). A glassy carbon electrode (GCE) was modified with a composite consisting of a poly(N-isopropylacrylamide)-chitosan microgel with incorporated palladium nanoparticles. The microgel was characterized by FE-SEM, EDX, XPS, FTIR, XRD, and EIS. The modified GCE is shown to enable direct electro-reductive determination of PEL by using differential pulse voltammetry. The method works in pH7 solution and in the 0.01μM to 1.3mM PEL concentration range. At a typical working potential of -0.66V (vs. Ag/AgCl) (at50mV/s), the detection limit is as low as 0.7 nM, and the electrochemical sensitivity is 1.60μAμM-1cm-2. Intriguingly, the modified GCE displays good recovery when applied to bok choy and water samples. Graphical abstract Schematic of an electrochemical method for determination of paraoxon ethyl (PEL) in bok choy extract and water by using poly(N-isopropyl acrylamide)-chitosan microgel decorated with palladium nanoparticle-modified glassy carbonelectrodes (PdNPs/PNIPAM-CT microgel/GCE).

Adsorption and detection of organic pollutants by fixed bed carbon nanotube electrochemical membrane

An electrically conductive, flow-through, fixed bed adsorption membrane (FCME) made of carbon nanotubes (CNT) installed in an electrochemical flow cell, was applied for the highly efficient adsorption and detection of organic pollutants. Three analytes with different chemical nature, i.e., parathion ethyl, tartrazine and diquat, were chosen as model systems to demonstrate the capabilities of the system. Adsorptive stripping voltammetry (AdSV) performed by the FCME provided directly the amount of analyte adsorbed; in contrast to an adsorption column, that monitors the effluent concentration. The adsorption capacity and kinetic constants were obtained by AdSV and were comparable with those predicted by the Thomas model. The FCME enabled the detection of nanomolar levels of tartrazine and parathion, and submicromolar levels of diquat with a linear range of three orders of magnitude. In addition to being a very sensitive analytical tool, FCME is an adsorption membrane that enables its simple electrochemical regeneration.

Electrochemical sensing and nano molar level detection of Bisphenol-A with molecularly imprinted polymer tailored on multiwalled carbon nanotubes

A rapid, effective and simple method for quantitative determination of Bisphenol-A (BPA) is important in environmental monitoring and health perspectives. In this work, a multi-walled carbon nanotube (MWCNT) based molecularly imprinted polymer (MIP) was successfully developed and used for modifying glassy carbon electrode (GCE) for the electrochemical detection of BPA. FTIR, Raman, XRD, SEM and AFM techniques were used for confirming the stepwise modifications in each stage. A well defined electrochemical response was obtained for BPA in cyclic voltammetry and differential pulse voltammetry. The influence of accumulation time and pH was studied and optimized. The electro catalytic sensing of BPA is possible with accessible range from 400.00 μM to 0.10 nM with detection limit of 0.02 nM. The stability, reproducibility and repeatability of the MIP/GCE sensor were also investigated. The applicability of the synthesized sensor in real life situation was confirmed by quantifying the amount of BPA in baby feeding bottle extracts.

Nanomolar Level Detection of Uric Acid in Blood Serum and Pest-Infested Grain Samples by an Amphiphilic Probe.

A pyrene based amphiphilic receptor has been utilized in the nanomolar detection of uric acid at physiological pH in water. The compound shows a unique concentration-dependent modulation in optical response toward uric acid. In intramolecular/static excimer form (low concentration range), it displays a ratiometric response, while a "turn-off" sensing is observed specifically in the presence of intermolecular/dynamic excimer (high concentration range). The present protocol is then employed for the estimation of uric acid in blood serum samples of healthy individuals. Bland-Altman analysis in comparison to clinically approved uricase assay indicated the high accuracy of the present method. Additionally, the extent of insect infestation in stored grain samples was determined by measuring the uric acid content of their aqueous extracts. Low-cost color strips were developed for on-site detection of uric acid without involving any sophisticated instrument or trained personnel.