On-Off-On Fluorometric Detection of Hg(II) and L-Cysteine Using Red Emissive Nitrogen-Doped Carbon Dots for Environmental and Clinical Sample Analysis.

This research introduces a novel fluorescence sensor 'on-off-on' employing nitrogen-doped carbon dots (N-CDs) with an 'on-off-on' mechanism for the selective and sensitive detection of Hg(II) and L-cysteine (L-Cys). N-CDs was synthesized using citric acid as the carbon precursor and urea as the nitrogen source in dimethylformamide (DMF) solvent, resulting in red emissive characteristics under UV light. Comprehensive spectroscopic analyses, including UV-Vis, fluorescence, FT-IR, XRD, XPS, Raman, and Zeta potential techniques, validated the structural and optical characteristics of the synthesized N-CDs. The maximum excitation and emission of N-CDs were observed at 548 and 622 nm, respectively. The quantum yield of N-CDs was calculated to be 16.1%. The fluorescence of N-CDs effectively quenches upon the addition of Hg(II) due to the strong coordination between Hg(II) and the surface functionalities of N-CDs. Conversely, upon the subsequent addition of L-Cys, the fluorescence of N-CDs was restored. This restoration can be attributed to the stronger affinity of the -SH group in L-Cys towards Hg(II) relative to the surface functionalities of N-CDs. This dual-mode response enabled the detection of Hg(II) and L-Cys with impressive detection limits of 15.1 nM and 8.0 nM, respectively. This sensor methodology effectively detects Hg(II) in lake water samples and L-Cys levels in human urine, with a recovery range between 99 and 101%. Furthermore, the N-CDs demonstrated excellent stability, high sensitivity, and selectivity, making them a promising fluorescence on-off-on probe for both environmental monitoring of Hg(II) and clinical diagnostics of L-Cys.

Turn-Off Fluorometric Determination of Bilirubin Using Facile Synthesized Nitrogen-Doped Carbon Dots as a Fluorescent Probe.

Bilirubin plays a significant role in human health management, particularly in the case of jaundice. Because of the need for the monitoring of bilirubin levels in jaundice patients, the development of a robust sensitive method becomes essential. Here, we describe the development of a highly sensitive and selective turn-off fluorometric detection method for bilirubin in blood serum samples using nitrogen-doped carbon dots (N-CDs). N-CDs was synthesized by the pyrolysis process, using citric acid and L-asparagine as the carbon and nitrogen sources, respectively. The prepared N-CDs solution showed highly intense blue emission with good stability. The HR-TEM image of N-CDs revealed spherical dot-like structures with an average size calculated to be 7.16 nm. Further, the surface functional groups of N-CDs were analyzed by FT-IR, Raman, XRD, and XPS techniques. Fluorescence spectra showed the maximum emission intensity at 443 nm (λex). The linear range of addition was performed from 1 to 150 µM, and the limit of detection (LOD) was determined to be 1.97 nM. The emission of N-CDs was quenched by Förster Resonance Energy Transfer (FRET) by adding bilirubin. These N-CDs showed extraordinary sensitivity and selectivity in the detection of bilirubin. Hence, this fluorescent probe has been proven successful in detecting the concentration of free bilirubin in human serum samples.

Direct Adsorption of Graphene Oxide on a Glassy Carbon Electrode: An Investigation of Its Adsorption and Electrochemical Activity.

Different modes of attachment of graphene oxide (GO) on an electrode surface resulted in unusual catalytic behavior respective of attachment because of film thickness. The present work investigates the direct adsorption of GO to the surface of a glassy carbon (GC) electrode. Scanning electron microscopy images revealed that multilayers of GO get adsorbed on the GC substrate and the adsorption was limited by folding up of the GO sheets at their edges. π-π and hydrogen bonding interactions between the GO and GC substrate flagged the adsorption of GO. pH studies revealed that higher adsorption of GO was achieved at pH = 3 rather than at pH = 7 and 10. Even though the electroactive surface area of adsorbed GO (GOads) was not remarkable (0.069 cm2), upon electrochemical reduction of GOads (Er-GOads), the electroactive surface area was escalated to be 0.174 cm2. Similarly, the RCT of Er-GOads was boosted to 2.9 kΩ compared to GOads which is 19 kΩ. Open circuit voltage was recorded to study the adsorption of GO on the GC electrode. Multilayered GO best fitted with the Freundlich adsorption isotherm, and the Freundlich constants like n and KF were found to be 4 and 0.992, respectively. The Freundlich constant "n" revealed the adsorption of GO on the GC substrate to be a physisorption process. Furthermore, the electrocatalytic performance of Er-GOads was demonstrated by taking uric acid as a probe. The modified electrode showed excellent stability toward the determination of uric acid.

Hybridization of Co3S4 and Graphitic Carbon Nitride Nanosheets for High-performance Nonenzymatic Sensing of H2O2.

The development of efficient H2O2 sensors is crucial because of their multiple functions inside and outside the biological system and the adverse effects that a higher concentration can cause. This work reports a highly sensitive and selective non-enzymatic electrochemical H2O2 sensor achieved through the hybridization of Co3S4 and graphitic carbon nitride nanosheets (GCNNS). The Co3S4 is synthesized via a hydrothermal method, and the bulk g-C3N4 (b-GCN) is prepared by the thermal polycondensation of melamine. The as-prepared b-GCN is exfoliated into nanosheets using solvent exfoliation, and the composite with Co3S4 is formed during nanosheet formation. Compared to the performances of pure components, the hybrid structure demonstrates excellent electroreduction towards H2O2. We investigate the H2O2-sensing performance of the composite by cyclic voltammetry, differential pulse voltammetry, and amperometry. As an amperometric sensor, the Co3S4/GCNNS exhibits high sensitivity over a broad linear range from 10 nM to 1.5 mM H2O2 with a high detection limit of 70 nM and fast response of 3 s. The excellent electrocatalytic properties of the composite strengthen its potential application as a sensor to monitor H2O2 in real samples. The remarkable enhancement of the electrocatalytic activity of the composite for H2O2 reduction is attributed to the synergistic effect between Co3S4 and GCNNS.

Probing the Interaction of Heavy and Transition Metal Ions with Silver Nanoparticles Decorated on Graphene Quantum Dots by Spectroscopic and Microscopic Methods.

We report a comprehensive study of the interaction of transition and heavy metal ions with graphene quantum dots-capped silver nanoparticles (AgGQDs) using different spectroscopic and microscopic techniques. High-resolution transmission electron microscopy studies show that the interaction of metal ions with AgGQDs leads to the formation of metal oxides, the formation of zerovalent metals, and the aggregation of Ag nanoparticles (AgNPs). The metal ions may interact with AgGQDs through selective coordination with -OH and -COOH functionalities, adsorption on the graphene moiety, and directly to AgNPs. For instance, the interaction of Cd2+ with AgGQDs altered the spherical shape of AgNPs into a chain-like structure. On the contrary, the formation of PbO is observed after the addition of Pb2+ to AgGQDs. Interestingly, the interaction of AgGQDs with Hg2+ results in the complete dissolution of Ag0 from the surface of GQDs and subsequent deposition of Hg0 on the graphene moiety of GQDs. Unlike transition metal ions, Cd2+, Pb2+, and Hg2+ can adsorb strongly on the graphene surface at the bridge, hollow, and top sites, respectively. This special interaction of heavy metal ions with the graphene surface would decide the mechanistic pathway in which the reaction proceeds. The transition metal ions Cu2+, Zn2+, Co3+, Mn2+, Ni2+, and Fe3+ induced the aggregation of AgNPs.

Systematic Study on Morphological, Electrochemical Impedance, and Electrocatalytic Activity of Graphitic Carbon Nitride Modified on a Glassy Carbon Substrate from Sequential Exfoliation in Water.

Several researchers have synthesized graphitic carbon nitride (GCN) from various precursors and attached it to electrode substrates after exfoliation under different conditions and have reported inconsistent data on electrochemical impedance, electroactive surface areas, and electrocatalytic activity. Thus, the present study aims to study the same systematically in addition to morphology after modifying GCN on the GC substrate from different exfoliation times in water assisted by sonication. The GCN was prepared from urea by bulk condensation pyrolysis and then attached to the GC substrate by drop casting to study its morphology, electrochemical impedance, and electrocatalytic activity with respect to exfoliation. The SEM image of a GCN-modified GC plate after 15 and 30 min of exfoliation shows bulky structure whereas thin sheets of GCN were noticed after 120 min of exfoliation. On the other hand, broken sheets were observed when GCN was coated from beyond 120 min of exfoliation. The electrochemical impedance studies show that the charge transfer resistance (RCT) of GCN modified from 15 and 30 min of exfoliation was higher than that for the bare GC electrode. However, it started to decrease while increasing the exfoliation time, and 1.8 kΩ was obtained after 120 min of exfoliation. The RCT value was again increased to 3.2 and 5.0 kΩ for GCN coated after 150 and 180 min of exfoliation, respectively. The electroactive surface area (EASA) of GCN modified by 15 and 30 min of exfoliation was less than that of the bare GC electrode, whereas it was 3.8-fold higher for GCN coated from 120 min of exfoliation. The electrocatalytic activity of the GC electrodes modified with GCN was then tested by studying ascorbic acid (AA) and dopamine (DA) oxidation and reduction of hydrogen peroxide (HP). Among the different exfoliation times, GCN modified from 120 min of exfoliation displayed the highest electrocatalytic activity toward AA, DA, and HP. This was attributed to its higher EASA and lower charge-transfer resistance.

Unusual Reactivity of Graphene Quantum Dot-Wrapped Silver Nanoparticles with Hg(II): Spontaneous Growth of Hg Flowers and Their Electrocatalytic Activity.

The galvanic reaction (GR) between a graphene quantum dot (GQD)-stabilized AgNP (Ag-GQD)-modified glassy carbon (GC) surface and Hg(II) leads to complete dissolution of AgNPs within 15 min and subsequent growth of Hg(0) as a "flower" on the GQD surface. This is unusual because generally the GR of bulk Ag/AgNPs with Hg(II) leads to the formation of a Hg-Ag amalgam/core shell structure. The appearance of peaks at 99.9 and 103.9 eV in X-ray photoelectron spectroscopy confirms Hg(0) on GQDs, whereas the disappearance of a peak at 370 eV indicates complete dissolution of Ag(0). When 200 ppm Hg(II) interacts with Ag-GQDs for 10 min, coalescence of AgNPs takes place along with the formation of Hg(0) petals separately. However, Hg(0) is grown as a flower with 2 µm size, and complete dissolution of AgNPs occurs subsequently after 15 min. The reason for anti-amalgamation is the direct deposition of Hg(0) by the available oxygen functional groups, followed by its strong adsorption on the graphene surface of GQDs. The subsequent growth of Hg(0) as a flower is due to the GR between AgNPs and Hg(II). Interestingly, the Hg flower-GQD-modified GC electrode acts as a good electrocatalyst toward H2O2 reduction by decreasing its overpotential by 150 mV in contrast to GC/Ag-GQDs.

Formation of Mercury Droplets at Ambient Conditions through the Interaction of Hg(II) with Graphene Quantum Dots.

Unlike other metals, Hg forms droplets at ambient conditions when a Hg(II) salt interacts with hydroxyl-enriched graphene quantum dots (HEGQDs). The hydroxylation of GQD surface is evident from FT-IR, Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS) techniques. The scanning electron microscopy images of Hg(II)-HEGQDs incubated for 0, 1, 24, and 168 h show Hg droplets with the size of 0.1, 0.3, 0.8, and 2 µm, respectively. The XPS studies confirm the presence of Hg(0) and also reveal a noticeable decline in the composition percentage of C-O, whereas a marked increase is observed in the C═O composition percentage. The pathway for the formation of droplets induces immediate reduction of Hg(II) to Hg(0) by both hydroxyl groups and π electron cloud present on the surface of HEGQDs, followed by coalescence. The formed Hg(0) is then strongly adsorbed on the hollow sites of graphene and acts as a nucleation site for the growth of droplets. The kinetics of the reaction obeys LaMer Burst nucleation followed by coalescent growth in addition to autocatalytic reduction and finally follows the Oswald ripening mechanism. The internal pressure of Hg droplets gradually decreases as the radius of the drop increases over the incubation time and liquid-rhombohedral transformation is likely to take place at a radius of 0.8 nm.

Electrocatalyst based on Ni-MOF intercalated with amino acid-functionalized graphene nanoplatelets for the determination of endocrine disruptor bisphenol A.

In this study, controlled growth of Ni-MOF was decorated in amino acid-functionalized graphene nanoplatelets (FxGnP) by a solvothermal approach. The synthesized nanocomposite was characterized by various spectral, microscopic, and electrochemical techniques. FE-SEM and TEM image results exhibited the sheet-like structure of FxGnP and spherical-like Ni-MOF with an average size of 5.6 µm. Appreciably, the size of Ni-MOF was reduced to ∼2.3 µm while introducing the FxGnP. The presence of a large number of hydroxyl and epoxy functional groups of FxGnP acts as a nucleation center and restricted the uncontrolled growth of Ni-MOF. The FxGnP-Ni-MOF composite was modified on GCE and then utilized for the oxidation of bisphenol A (BPA). The nanocomposite material showed a sharp peak at +0.38 V vs. Ag/AgCl (saturated NaCl) with a stable response for BPA due to their less particle size with high electroactive surface area and higher electrical conductance, whereas bare GCE failed to the stable determination of BPA. The developed assay for determination of BPA exhibited a wide linear range from 2 × 10-9 M to 10 × 10-6 M, LOD 0.184 × 10-9 M and sensitivity of 247.65 µA mM-1 cm-2. The FxGnP-Ni-MOF/GCE showed good stability and reproducibility against BPA. Finally, the present electrocatalyst was effectively utilized for the quantitative determination of BPA in water samples and obtained results were validated with HPLC method.

Fabrication of low-cost sustainable electrocatalyst: a diagnostic tool for multifunctional disorders in human fluids.

In purine metabolism, the xanthine oxidoreductase enzyme converts hypoxanthine (HXN) to xanthine (XN) and XN to uric acid (UA). This leads to the deposition of UA crystals in several parts of the body and the serum UA level might be associated with various multifunctional disorders. The dietary intake of caffeine (CF) and ascorbic acid (AA) decreases the UA level in the serum, which leads to cellular damage. Hence, it is highly needed to monitor the UA level in the presence of AA, XN, HXN, and CF and vice versa. Considering this sequence of complications, the present paper reports the fabrication of an electrochemical sensor using low-cost N-doped carbon dots (CDs) for the selective and simultaneous determination of UA in the presence of AA, XN, HXN, and CF at the physiological pH. The colloidal solution of CDs was prepared by the pyrolysis of asparagine and fabricated on a GC electrode by cycling the potential from -0.20 to +1.2 V in a solution containing CDs and 0.01 M H2SO4. Here, the surface -NH2 functionalities of CDs were used to make a thin film of CDs on the GC electrode. FT-IR spectroscopy confirmed the involvement of the -NH2 group in the formation of the CD film. HR-TEM analysis depicts that the formed CDs showed spherical particles with a size of 1.67 nm and SEM analysis exhibits the 89 nm CD film on the GC electrode surface. The fabricated CD film was successfully used for the sensitive and selective determination of UA. The determination of UA was achieved selectively in a mixture consisting of AA, XN, HXN, and CF with 50-fold high concentration. The CDs-film fabricated electrode has several benefits over the bare electrode: (i) well-resolved oxidation peaks for five analytes, (ii) boosted sensitivity, (iii) shifted oxidation as well as on-set potentials toward less positive potentials, and (iv) high stability. The practical utility of the present sensor was tested by simultaneously determining the multifactorial disorders-causing agents in human fluids. The electrocatalyst developed in the present study is sustainable and can be used for multiple analyses; besides, the electrochemical method used for the fabrication of the CD film is environmentally benign.

Ultrasonic Assisted Synthesis of Size-Controlled Cu-Metal-Organic Framework Decorated Graphene Oxide Composite: Sustainable Electrocatalyst for the Trace-Level Determination of Nitrite in Environmental Water Samples.

Excess levels of nitrite ion in drinking water interact with amine functionalized compounds to form carcinogenic nitrosamines, which cause stomach cancer. Thus, it is indispensable to develop a simple protocol to detect nitrite. In this paper, a Cu-metal-organic framework (Cu-MOF) with graphene oxide (GO) composite was synthesized by ultrasonication followed by solvothermal method and then fabricated on a glassy carbon (GC) electrode for the sensitive and selective determination of nitrite contamination. The SEM image of the synthesized Cu-MOF showed colloidosome-like structure with an average size of 8 µm. Interestingly, the Cu-MOF-GO composite synthesized by ultrasonic irradiation followed by solvothermal process produce controlled size of 3 µm colloidosome-like structure. This was attributed to the formation of an exfoliated sheet-like structure of GO by ultrasonication in addition to the obvious influence of GO providing the oxygen functional groups as a nucleation node for size-controlled growth. On the other hand, the composite prepared without ultrasonication exhibited 6.6 µm size agglomerated colloidosome-like structures, indicating the crucial role of ultrasonication for the formation of size-controlled composites. XPS results confirmed the presence of Cu(II) in the as-synthesized Cu-MOF-GO based on the binding energies at 935.5 eV for Cu 2p3/2 and 955.4 eV for Cu 2p1/2. The electrochemical impedance studies in [Fe(CN)6]3-/4- redox couple at the composite fabricated electrode exhibited more facile electron transfer than that with Cu-MOF and GO modified electrodes, which helped to utilize Cu-MOF-GO for trace level determination of nitrite in environmental effluent samples. The Cu-MOF-GO fabricated electrode offered a superior sensitive platform for nitrite determination than the Cu-MOF and GO modified electrodes demonstrating oxidation at less positive potential with enhanced oxidation current. The present sensor detects nitrite in the concentration range of 1 × 10-8 to 1 × 10-4 M with the lowest limit of detection (LOD) of 1.47 nM (S/N = 3). Finally, the present Cu-MOF-GO electrode was successfully exploited for nitrite ion determination in lake and dye contaminated water samples.

Correction to "Nitrogen-Doped Graphene Quantum-Dot Combined Sodium 10-Amino-2-methoxyundecanoate: Studies of Proinflammatory Gene Expression and Live Cell Imaging".

[This corrects the article DOI: 10.1021/acsomega.8b02085.].

Leaching of AuNPs from the surface of GO: Sensitive turn on fluorescence detection of toxic preservative.

Development of a novel colorimetric and turn-on fluorescent sensor for potassium metabisulphite (KMS) using graphene oxide stabilized gold nanoparticles (GO-AuNPs) was described. The red color GO-AuNPs was changed to violet while adding 250 × 10-5 M KMS whereas the absorbance band at 523 nm was decreased. The observed changes were ascribed to the leaching of AuNPs from GO. The emission maximum was observed at 448 nm for GO while exciting at 335 nm. However, the GO emission was "turn-off" after the formation of AuNPs on GO surface due to masking of oxygen functional groups responsible for emission. Interestingly, the emission of GO-AuNPs becomes "turn-on" after the addition of 75 × 10-6 M KMS. Further addition of KMS from 150 to 1125 × 10-6 M, the emission intensity of GO-AuNPs linearly increases with the correlation coefficient of 0.9980 and the limit of detection was found to be 9.4 µM L-1/1.2 mg L-1 (S/N = 3).

Water-soluble MoS2 quantum dots as effective fluorescence probe for the determination of bilirubin in human fluids.

Bilirubin is an important biomarker in the diagnosis and prognosis of patients with liver disorders. Herein, we report a simple, rapid, sensitive and selective quantitative determination of bilirubin using molybdenum disulfide quantum dots (MoS2 QDs) as a probe. The MoS2 QDs were synthesized through a hydrothermal route by using sodium molybdate and cysteine as the starting materials. The obtained MoS2 QDs exhibits strong luminescence property and excellent stability. The HR-TEM image shows that the size of the prepared MoS2 QDs was 2.4 nm with a spherical morphology. The MoS2 QDs emit intense blue photoluminescence (with excitation/emission peaks at 310/392 nm) under UV light and the fluorescence of MoS2 QDs was drastically quenched by the addition of bilirubin. The Förster resonance energy transfer (FRET) and inner filter effect (IFE) between MoS2 QDs and bilirubin resulted in the fluorescence quenching of MoS2 QDs. The present method demonstrated high sensitivity towards bilirubin with the limit of detection (LOD) of 2.1 nM (S/N = 3). The MoS2 QDs probe showed remarkable selectivity to bilirubin over other possible interferences. Moreover, the present fluorophore was successfully utilized for the detection of bilirubin in human serum and urine samples. QDs based fluorescence probe for the recognition of bilirubin is reported for the first time.

Carbon dots stabilized silver-lipid nano hybrids for sensitive label free DNA detection.

Carbon dots have been extensively used for the development of fluorescent based molecular affinity sensors. However, label free DNA sensing by electrochemical method is not reported so far. Herein, we report carbon dots stabilized silver nanoparticles (CD-AgNPs) lipid nano hybrids as a sensitive and selective platform for label free electrochemical DNA sensing. The CD-AgNPs were synthesized by wet chemical method and then characterized by UV-visible, Fourier-transform Infra-red (FT-IR), dynamic light scattering (DLS) and high resolution transmission electron microscopy (HR-TEM) techniques. These CD-AgNPs were used for decorating the binary lipid 1,2-dioleoyl-sn-glycero-3-phosphoethanolamine (DOPE) and N-[1-(2,3-Dioleoyloxy)propyl]-N,N,N-trimethylammonium chloride (DOTAP) surface (named as lipid) and tethered on self-assembled monolayer of 3-mercaptopropionic acid (MPA) (MPA-lipid-CD-AgNPs). The formation of array of MPA-lipid-CD-AgNPs on Au electrode was confirmed by atomic force microscopy (AFM). Electrochemical behavior of MPA- lipid-CD-AgNPs was monitored in the presence of 1 mM potassium ferri/ferrocyanide (K3/K4 [Fe(CN)6]). The formation of layer-by-layer MPA-lipid-CD-AgNPs is indicated by increased anodic and cathodic peak (ΔEp) separation with decreased redox peak current of K3/K4 [Fe(CN)6]. Short chain DNA (30 mer oligonucleotide, representing the lung cancer) was used as a model system for label free DNA sensing. Un-hybridized (single stranded DNA), hybridized (complementary hybridized), single, double and triple base mismatched target DNA hybridized surfaces were efficiently discriminated at 1 µM target DNA concentration at the Au/MPA-lipid-CD-AgNPs electrode by change in the charge transfer resistance from impedance technique. Further, the modified electrode was successfully used to determine target DNA in a wide linear range from 10-16 to 10-11 M. The present work open doors for the utilization of CDs in molecular affinity based electrochemical sensor design and development.

Silver nanoparticles capped with carbon dots as a fluorescent probe for the highly sensitive "off-on" sensing of sulfide ions in water.

The present study illustrates the synthesis of silver nanoparticles capped with carbon dots (AgNPs-CDs) and their application towards the sensitive and selective sensing of sulfide ions by colorimetry and spectrofluorimetry methods. The CDs were prepared from l-asparagine by pyrolysis at 234 °C. The as-synthesized CDs were then utilized as reducing and capping agents for the synthesis of AgNPs-CDs by the wet chemical method. The size of the AgNPs-CDs was found to be ~ 5.2 nm. They show a characteristic surface plasmon resonance band at 417 nm and emission maximum at 441 nm when excited at 348 nm. Since the AgNPs were formed on the surface of CDs, the emission intensity of AgNPs-CDs was drastically decreased in contrast to that of CDs. The as-synthesized AgNPs-CDs were then successfully used for the sensitive and selective determination of sulfide ions. The addition of 0.1 µM sulfide ions to AgNPs-CDs leads to a decrease in the absorbance intensity at 417 nm aside turning from yellow to colorless. In the contrary, the emission was "turned on" after the addition of sulfide ions. The decrease in the absorbance and increase in the emission were attributed to the rapid formation of Ag2S. Finally, the practical application of the present method was demonstrated by determining dissolved H2S in tap water samples.

Nitrogen-Doped Graphene Quantum Dot-Combined Sodium 10-Amino-2-methoxyundecanoate: Studies of Proinflammatory Gene Expression and Live Cell Imaging.

Marine cyanobacteria are renowned for producing bioactive secondary metabolites with great structural diversity via mixed biosynthetic pathways. Lyngbya sp., a marine cyanobacterium, produces many metabolites with anti-inflammatory potentials; nevertheless, its bioactive metabolites exercising providing protection against inflammation has been deciphered inadequate. In this study, the ethanolic fraction of the Lyngbya sp. extract was purified and identified as sodium 10-amino-2-methoxyundecanoate (SAM) using Fourier-transform infrared spectroscopy, nuclear magnetic resonance, and electron spray ionization-mass spectroscopy. SAM showed prominent inhibition of inflammation, which was analyzed by reactive oxygen species generation and nitric oxide (NO) inhibition assay. Furthermore, the anti-inflammatory potentials of SAM were evaluated in lipopolysaccharide (LPS)-induced RAW 264.7 macrophage cell lines by fluorescence-activated cell sorting analysis, which evidenced prominent decrease in COX-2 expression (∼90%) with SAM-treated cells than the control. Subsequently, a semiquantitative real-time polymerase chain reaction analysis also revealed the downregulation of COX-2, iNOS, TNF-α, NF-κß, IL-1α, IL-1ß, IL-4, and IL-6 gene expression in SAM-treated LPS-induced RAW 264.7 cells. To further enhance the delivery of SAM into the cells, it was combined with N-doped graphene quantum dots (N-GQDs) for the anti-inflammatory potentials. It resulted in improved downregulation of COX-2, iNOS, TNF-α, NF-κß, IL-1α, IL-1ß, IL-4, and IL-6 than cells treated with SAM alone. Conclusively, N-GQDs combined with SAM have the effective therapeutic potential as an inhibitor of inflammation by modulating the expression of different cytokine genes.

Fluorogenic mercury ion sensor based on pyrene-amino mercapto thiadiazole unit.

A highly selective and sensitive determination of Hg2+ in water samples with bioimaging applications in living cells using a fluorogenic pyrene-amino mercapto thiadiazole (PYAMT) probe is described. The probe PYAMT exhibited three absorption peaks at 333, 348 and 394nm and emission maxima at 378, 388 and 397nm (λex=348nm). It showed significant fluorescent quenching (96%) with I/I0=0.051 upon the addition of 2.5µM Hg2+ ion in CH3CN(ACN):H2O (1:1, v/v; pH 7.2), whereas its fluorescence remained unaltered in the presence of other metal ions. The quenching phenomenon is attributed to the heavy atom effect of Hg2+ ion followed by electron transfer. The fluorescence intensity decreased linearly against a wide range from 100nM to 2.5µM Hg2+ (R2=0.9937) with a limit of detection as low as 0.35nM (S/N=3). The binding stoichiometry ratio of PYAMT-Hg2+ is proved to be 1:1 by fluorescence and DFT measurements. The sensor possesses high association constant with Hg2+ ion in the order of 9.08×105M-1 and it is also capable of reversibly detecting cysteine with OFF-ON mechanism. Finally, the proposed method is successfully applied to selectively detect Hg2+ ion in real water samples and bioimaging studies in live cells.

Naked eye and spectrophotometric detection of chromogenic insecticide in aquaculture using amine functionalized gold nanoparticles in the presence of major interferents.

Detection of a chromogenic insecticide, malachite green (MG) using 3,5-diamino-1,2,4-triazole capped gold nanoparticles (DAT-AuNPs) by both naked eye and spectrophotometry was described in this paper. The DAT-AuNPs were prepared by wet chemical method and show absorption maximum at 518nm. The zeta potential of DAT-AuNPs was found to be -39.9mV, suggesting that one of the amine groups of DAT adsorbed on the surface of AuNPs and the other amine group stabilizes the AuNPs from aggregation. The wine red color DAT-AuNPs changes to violet while adding 25µM MG whereas the absorption band at 518nm was increased and shifted towards longer wavelength. However, addition of 70µM MG leads to the aggregation of DAT-AuNPs. This is due to strong electrostatic interaction between ammonium ion of MG and the free amine group of DAT. Based on the color change and shift in SPR band, 25 and 5µM MG can be easily detected by naked eye and spectrophotometry. The DAT-AuNPs show high selectivity towards MG even in the presence of 5000-fold higher concentrations of common interferents. The practical application was successfully demonstrated by determining MG in fish farm water.

A novel pyrene based fluorescent probe for selective detection of cysteine in presence of other bio-thiols in living cells.

This manuscript reports the synthesis of pyrene-based fluorescent probe (PA-1) containing α,ß-unsaturated carbonyl moiety and its application towards the selective and sensitive detection of cysteine (Cys) over other bio-thiols. The probe, 3-(2-hydroxyphenyl)-1-pyrenyl-2-propenone (PA-1) was synthesized through Claisen-Schmidt condensation between acetyl pyrene and salicylaldehyde. The formed product was characterized by (1)H NMR, (13)C NMR and GC-MS techniques. The probe exhibited absorption maximum at 374nm and emission maximum at 467nm (λex=342nm). The emission intensity of PA-1 was greatly enhanced while adding 2.5nM Cys. This can be attributed to the nucleophilic attack of Cys to the α,ß-unsaturated ketone resulting in switching off, intramolecular charge transfer (ICT) from pyrene moiety to the phenolic nucleus. This was confirmed by DFT measurements. The PA-1 exhibited an excellent selectivity towards the determination of 40nM cys in the presence of 250,000-fold higher concentration of common interferents. The emission intensity was linearly increased and the limit of detection was found to be 10pM/L (S/N=3). Interestingly, the response of the PA-1 towards Cys is less than 1min. The confocal laser scanning micrographs of HeLa cells confirmed the cell permeability of the PA-1 and its ability to selectively detect Cys in living cells. In addition, the proposed probe was successfully applied for the determination of Cys in blood serum samples.