Orange-Red-Emitting Carbon Dots for Bilirubin Detection and Its Antibacterial Activity Against Escherichia coli and Staphylococcus aureus

In this study, orange-red-emitting carbon dots (OR-CDs) were prepared from p-phenylenediamine (p-PDA) and urea as starting precursors through the hydrothermal method. The OR-CDs exhibited bright orange-red fluorescence at 618 nm when excited at 480 nm. The obtained OR-CDs exhibited stable photophysical properties under different physiological conditions. The unique photophysical property of OR-CDs were then utilized for fluorometric determination of bilirubin. The fluorometric assay revealed that the fluorescence intensity of OR-CDs is gradually quenched upon the addition of bilirubin (1-20 μM). The mechanism of fluorescence quenching was evaluated by steady-state fluorescence analysis and time-correlated single photon counting measurements. The OR-CDs showed good selectivity and sensitivity toward bilirubin over other common interfering biomolecules. The present fluorometric assay showed a linear response toward bilirubin between 1 and 10 μM with a limit of detection of 4.80 nM. Further, a fluorescence test cotton swab-based detection probe has been successfully developed by incorporating OR-CDs for the point-of-care detection of bilirubin in biofluids. Furthermore, a light-emitting diode light that emits orange-red light was prepared by embedding the OR-CDs within the poly(vinyl alcohol) polymer matrix. Moreover, the antibacterial activity of OR-CDs was tested against Gram-negative Escherichia coli and Gram-positive Staphylococcus aureus. The antibacterial efficacy of OR-CDs was demonstrated by various mechanisms, such as reactive oxygen species generation, destruction of cell structure, chemical binding to membrane, and surface wrapping. Interestingly, the survival assay against L929 fibroblast cells exhibits favorable biocompatibility and bioimaging.

Nanoarchitectonics of graphene based sensors for food safety monitoring

Since the desire for the real-time food quality monitoring, plenty of research effort has been made to develop novel tools and to offer extremely efficient detection of food contaminants. Unique electrical, mechanical, and thermal properties make graphene an important material in the field of sensor research. The material can be manufactured into flakes, sheets, films and with its oxidized derivatives could be almost used for a limitless set of application. Herein, current graphene-based sensors for food quality monitoring, novel designs, sensing mechanisms and elements of sensor systems and potential challenges will be outlined and discussed.

Evolution of Diagnostic Methods for Helicobacter pylori Infections: From Traditional Tests to High Technology, Advanced Sensitivity and Discrimination Tools

Rapid diagnosis and treatment application in the early stages of H. pylori infection plays an important part in inhibiting the transmission of this infection as this bacterium is involved in various gastric pathologies such as gastritis, gastro-duodenal ulcer, and even gastric neoplasia. This review is devoted to a quick overview of conventional and advanced detection techniques successfully applied to the detection of H. pylori in the context of a compelling need to upgrade the standards of the diagnostic methods which are currently being used. Selecting the best diagnostic method implies evaluating different features, the use of one or another test depending on accessibility, laboratories equipment, and the clinical conditions of patients. This paper aims to expose the diagnosis methods for H. pylori that are currently available, highlighting their assets and limitations. The perspectives and the advantages of nanotechnology along with the concept of nano(bio)sensors and the development of lab-on-chip devices as advanced tools for H. pylori detection, differentiation, and discrimination is also presented, by emphasizing multiple advantages: simple, fast, cost-effective, portable, miniaturized, small volume of samples required, highly sensitive, and selective. It is generally accepted that the development of intelligent sensors will completely revolutionize the acquisition procedure and medical decision in the framework of smart healthcare monitoring systems.

Synthetic Approaches, Modification Strategies and the Application of Quantum Dots in the Sensing of Priority Pollutants

Polycyclic aromatic hydrocarbons (PAHs) and nitro-aromatic compounds (NACs) are two classifications of environmental pollutants that have become a source of health concerns. As a result, there have been several efforts towards the development of analytical methods that are efficient and affordable that can sense these pollutants. In recent decades, a wide range of techniques has been developed for the detection of pollutants present in the environment. Among these different techniques, the use of semiconductor nanomaterials, also known as quantum dots, has continued to gain more attention in sensing because of the optical properties that make them useful in the identification and differentiation of pollutants in water bodies. Reported studies have shown great improvement in the sensing of these pollutants. This review article starts with an introduction on two types of organic pollutants, namely polycyclic aromatic hydrocarbons and nitro-aromatic explosives. This is then followed by different quantum dots used in sensing applications. Then, a detailed discussion on different groups of quantum dots, such as carbon-based quantum dots, binary and ternary quantum dots and quantum dot composites, and their application in the sensing of organic pollutants is presented. Different studies on the comparison of water-soluble quantum dots and organic-soluble quantum dots of a fluorescence sensing mechanism are reviewed. Then, different approaches on the improvement of their sensitivity and selectivity in addition to challenges associated with some of these approaches are also discussed. The review is concluded by looking at different mechanisms in the sensing of polycyclic aromatic hydrocarbons and nitro-aromatic compounds.

Aggregation-based fluorescence amplification strategy: "turn-on" sensing of aminoglycosides using near-IR carbocyanine dyes and pre-micellar surfactants

This study is aimed at developing sensing schemes without obtaining selective receptors. A series of simple carbocyanine dyes was synthesized, whose emission was quenched in water with formation of nanoparticles in the range of 20-100 nm. Fluorescence in near-IR region is "turned on" in the presence of a drug cation of middle molecular weight (400-700 Da) and sodium dodecyl sulfate (SDS), as well as anionic drugs and a cationic surfactant (cetyltrimethylammonium bromide, CTAB). Aggregates (clusters) up to 100-200 nm in size were detected using dynamic light scattering (DLS) and Rayleigh light scattering (RLS) techniques in the systems: cationic analyte-SDS, carbocyanine dye-CTAB, and in all brightly fluorescent ternary systems dye-surfactant-analyte. Small ions (<200 Da) incapable of multi-point binding do not form the aggregates or cause the emission enhancement. The "turn-on" signal is only observed at the surfactant submicellar concentrations insufficient to solubilize the dye nanoparticles. Based on these findings, we suggest a rapid and simple method for the detection of ≥4·10^-5 mol/L of neomycin in urine. The proposed strategy paves the way for developing more selective methods.

A rapid, simple and ultrasensitive spectrofluorimetric method for the direct detection of metformin in real samples based on a nanoquenching approach

Metformin (MET), as an oral antidiabetic and antihyperglycemic agent, is widely used to treat type II diabetes mellitus. Because of its increasing consumption, developing a fast, simple, and selective method to determine its concentration in biological samples (serum and urine) and pharmaceutical formulations (tablets) is of great interest. In this study, we used a FRET-based fluorescent nanosensor (Tb-phen-AgNPs system) for sensitive detection of MET in tablet and serum samples. This method is based on the enhancing effect of MET on the emission intensity of the Tb-phen complex, which is quenched by AgNPs via energy transfer process (turn off-on mode). A good linear relationship between the MET concentration and enhanced emission intensity of the Tb-phen-AgNPs system was observed in the range of (0.75-3.7) × 10^-6 M under optimum conditions. Limit of detection and limit of quantitation were calculated to be 0.43 × 10^-6 M and 1.31 × 10^-6 M, respectively. This method was successfully used to determine MET concentrations in pharmaceutical dosage form and in spiked serum sample. The obtained recoveries from pharmaceutical formulation and serum sample were in the range 86.75-98.97% and 85.10-100.96%, respectively. Collectively, our results indicated that the method described here is simple, sensitive, cost effective, and free from interference. Therefore, it can be used as an effective and routine method for the direct and rapid determination of MET levels in biological samples such as serum.

A Review on the Use of Impedimetric Sensors for the Inspection of Food Quality

This paper exhibits a thorough review of the use of impedimetric sensors for the analysis of food quality. It helps to understand the contribution of some of the major types of impedimetric sensors that are used for this application. The deployment of impedimetric sensing prototypes has been advantageous due to their wide linear range of responses, detection of the target analyte at low concentrations, good stability, high accuracy and high reproducibility in the results. The choice of these sensors was classified on the basis of structure and the conductive material used to develop them. The first category included the use of nanomaterials such as graphene and metallic nanowires used to form the sensing devices. Different forms of graphene nanoparticles, such as nano-hybrids, nanosheets, and nano-powders, have been largely used to sense biomolecules in the micro-molar range. The use of conductive materials such as gold, copper, tungsten and tin to develop nanowire-based prototypes for the inspection of food quality has also been shown. The second category was based on conventional electromechanical circuits such as electronic noses and other smart systems. Within this sector, the standardized systems, such as electronic noses, and LC circuit -based systems have been explained. Finally, some of the challenges posed by the existing sensors have been listed out, along with an estimate of the increase in the number of sensors employed to assess food quality.

Aptasensor for multiplex detection of antibiotics based on FRET strategy combined with aptamer/graphene oxide complex

The development of a multiplexed sensing platform is necessary for highly selective, sensitive, and rapid screening of specific antibiotics. In this study, we designed a novel multiplex aptasensor for antibiotics by fluorescence resonance energy transfer (FRET) strategy using DNase I-assisted cyclic enzymatic signal amplification (CESA) method combined with aptamer/graphene oxide complex. The aptamers specific for sulfadimethoxine, kanamycin, and ampicillin were conjugated with Cyanine 3 (Cy3), 6-Carboxyfluorescein (FAM), and Cyanine 5 (Cy5), respectively, and graphene oxide (GO) was adopted to quench the fluorescence of the three different fluorophores with the efficiencies of 94.36%, 93.94%, and 96.97% for Cy3, FAM, and Cy5, respectively. CESA method was used for sensitive detection, resulting in a 2.1-fold increased signal compared to those of unamplified method. The aptasensor rapidly detected antibiotics in solution with limit of detection of 1.997, 2.664, and 2.337 ng/mL for sulfadimethoxine, kanamycin, and ampicillin, respectively. In addition, antibiotics dissolved in milk were efficiently detected with similar sensitivities. Multiplexed detection test proved that the fluorescently modified aptamers could work separately from each other. The results indicate that the aptasensor offers high specificity for each antibiotic and enables simultaneous and multicolor sensing for rapid screening of multiple antibiotics at the same time.

Smartphone-based kanamycin sensing with ratiometric FRET

FRET aptamer based kanamycin detection enables reusable and smartphone sensing.

An efficient fluorescence resonance energy transfer system from quantum dots to graphene oxide nano sheets: Application in a photoluminescence aptasensing probe for the sensitive detection of diazinon

In this paper a new aptasensor with high-sensitivity, and high-specificity for detection of diazinon, was discovered, based on fluorescence resonance energy transfer (FRET) between quantum dot (QD) as a donor and graphene oxide (GO) as an acceptor. l-cysteine capped CdS QDs/DF20 aptamer bioconjugates were successfully synthesized. GO was also attached to aptamers and photoluminescence quenching was obtained through FRET. By adding target diazinon to the bioconjugates containing GO, photoluminescence recovery was detected due to detachment of GO from the aptamer as a result of the difference in affinity for the aptamer. The detection limit of the biosensor was 0.13 nM and the linearity was maintained from 1.05 to 206 nM. Other pesticides and herbicides did not contribute to photoluminescence recovery due to lack of binding affinity for the aptamers, which demonstrates the selectivity of the biosensor. The results show the applicability of the aptasensor for monitoring diazinon in environmental and agricultural samples.

Click chemistry inspired copper sulphide nanoparticle-based fluorescence assay of kanamycin using DNA aptamer

A highly selective and sensitive fluorescence assay for kanamycin has been developed that depends on complementation of two splits of DNA aptamer. One DNA split was labeled with CuS nanoparticle and the other was decorated with biotin, which enabled coupling with streptavidin magnesphere paramagnetic particles (PMPs). Complementation of the two-aptamer splits happened only in the presence of kanamycin and the subsequent sandwich was separated via a magnet. The released Cu(II) was reduced to Cu(I) by sodium ascorbate and finally catalyzed the click reaction between fluorogenic 3-azido-7-hydroxycoumarin and propargyl alcohol to afford the corresponding fluorescent 1,4-disubstituted-1,2,3-triazole. The fluorescence signal produced (λ_ex. = 365 nm, λ_em. = 470 nm) was dependent on kanamycin concentration. Fluorescence signal amplification was found to be in good linear relationship with the logarithm of kanamycin concentration in the range of 0.04-20 nM. Furthermore, the proposed assay showed a good reproducibility, high selectivity and low detection limits for kanamycin determination. In addition, the capability of the proposed method to detect kanamycin in biological samples with satisfactory results was demonstrated.

A novel fluorescent biosensor for adrenaline detection and tyrosinase inhibitor screening

In this work, a novel simple fluorescent biosensor for the highly sensitive and selective detection of adrenaline was established. Firstly, water-soluble CuInS₂ quantum dots (QDs) capped by L-Cys were synthesized via a hydrothermal synthesis method. Then, the positively charged adrenaline was assembled on the surface of CuInS₂ QDs due to the electrostatic interactions and hydrogen bonding, which led to the formation of adrenaline-CuInS₂ QD (Adr-CuInS₂ QD) electrostatic complexes. Tyrosinase (TYR) can catalyze adrenaline to generate H₂O₂, and additionally oxidize the adrenaline to adrenaline quinone. Both the H₂O₂ and the adrenaline quinone can quench the fluorescence of the CuInS₂ QDs through the electron transfer (ET) process. Thus, the determination of adrenaline could be facilely achieved by taking advantage of the fluorescence "turn off" feature of CuInS₂ QDs. Under the optimum conditions, the fluorescence quenching ratio I_f/I_f0 (I_f and I_f0 were the fluorescence intensity of Adr-CuInS₂ QDs in the presence and absence of TYR, respectively) was proportional to the logarithm of adrenaline concentration in the range of 1 × 10^-8-1 × 10^-4 mol L^-1 with the detection limit of 3.6 nmol L^-1. The feasibility of the proposed biosensor in real sample assay was also studied and satisfactory results were obtained. Significantly, the proposed fluorescent biosensor can also be utilized to screen TYR inhibitors. Graphical abstract Schematic illustration of the fluorescent biosensor for adrenaline detection (A) and tyrosinase inhibitor screening (B).

Highly-sensitive aptasensor based on fluorescence resonance energy transfer between l-cysteine capped ZnS quantum dots and graphene oxide sheets for the determination of edifenphos fungicide

With the advantages of excellent optical properties and biocompatibility, single-strand DNA-functionalized quantum dots have been widely applied in biosensing and bioimaging. A new aptasensor with easy operation, high sensitivity, and high selectivity was developed by immobilizing the aptamer on water soluble l-cysteine capped ZnS quantum dots (QDs). Graphene oxide (GO) sheets are mixed with the aptamer-QDs. Consequently, the aptamer-conjugated QDs bind to the GO sheets to form a GO/aptamer-QDs ensemble. This aptasensor enables the energy transfer based on a fluorescence resonance energy transfer (FRET) from the QDs to the GO sheets, quenching the fluorescence of QDs. The GO/aptamer-QDs ensemble assay acts as a "turn-on'' fluorescent sensor for edifenphos (EDI) detection. When GO was replaced by EDI, the fluorescence of QDs was restored and its intensity was proportional to the EDI concentration. This GO-based aptasensor under the optimum conditions exhibited excellent analytical performance for EDI determination, ranging from 5×10^-4 to 6×10^-3mg L^-1 with the detection limit of 1.3×10^-4mgL^-1. Furthermore, the designed aptasensor exhibited excellent selectivity toward EDI compared to other pesticides and herbicides with similar structures such as diazinon, heptachlor, endrin, dieldrin, butachlor and chlordane. Good reproducibility and precision (RSD =3.9%, n =10) of the assay indicates the high potential of the aptasensor for quantitative trace analysis of EDI. Moreover, the results demonstrate the applicability of the aptasensor for monitoring EDI fungicide in spiked real samples.

Fluorescence sensor for detecting protamines based on competitive interactions of polyacrylic acid modified with sodium 4-amino-1-naphthalenesulfonate with protamines and aminated graphene oxide

An easy-to-use fluorescent probe for detecting protamines was developed.

Triple-helix molecular switch-induced hybridization chain reaction amplification for developing a universal and sensitive electrochemical aptasensor

In this work, a universal and sensitive “signal-on” electrochemical aptasensor platform has been developed based on a triple-helix molecular switch (THMS)-induced hybridization chain reaction (HCR) amplification.