A novel N-CNDs/PAni modified molecular imprinted polymer for ultraselective and sensitive detection of ciprofloxacin in lentic ecosystems: a dual responsive optical sensor

The research study describes the development of a hybrid nanocomposite called nitro-doped carbon nanodots/polyaniline/molecularly imprinted polymer (N-CNDs/PAni/MIP). This composite is specifically engineered to function as a durable and flexible dual-response sensor to detect and analyze pharmaceutical organic contaminants (POCs). Powder X-Ray diffraction (PXRD), Fourier transform infrared (FT-IR), thermogravimetric analysis (TGA), transmission electron microscopy (TEM), and scanning electron microscopy (SEM) were employed to perform an exhaustive structural and morphological analysis of N-CNDs/PAni/MIP. N-CNDs/PAni/MIP emitted blue luminescence under ultraviolet irradiation and exhibited typical excitation-dependent emission properties. It can act as fluorescent probe for the detection of CIPRO with high selectivity and sensitivity with an IF value of 4.2. Furthermore, N-CNDs/PAni/MIP exhibited high peroxidase-like catalytic behavior. After adding CIPRO to the N-CNDs/PAni/MIP/TMB/H2O2 system, the blue color of the solution faded due to the reduction of blue ox-TMB to colorless TMB. Based on these two phenomena, with CIPRO as the target analyte, the N-CNDs/PAni/MIP dual sensor showed a minimal detection limit of 70 pM for the fluorescent signaling platform and 3.5 nM for the colorimetric probe with a linear range of 0.038-200 nM. The fluorometric and colorimetric assays based on N-CNDs/PAni/MIP for CIPRO detection were then successfully applied to lentic water as well as to tap water samples, demonstrating the sensitivity and dependability of the instrument. Furthermore, the synthesized PVA (N-CNDs/PAni/MIP) films enable the recognition of CIPRO, and these films have the potential to be integrated into portable sensing devices, providing a practical solution for rapid and on-site detection of CIPRO in various samples.

Carbon Dots and Their Polymeric Nanocomposites: Insight into Their Synthesis, Photoluminescence Mechanisms, and Recent Trends in Sensing Applications

Carbon dots (CDs), a novel class of carbon-based nanoparticles, have received a lot of interest recently due to their exceptional mechanical, chemical, and fluorescent properties, as well as their excellent photostability and biocompatibility. CDs' emission properties have already found a variety of potential applications, in which bioimaging and sensing are major highlights. It is widely acknowledged that CDs' fluorescence and surface conditions are closely linked. However, due to the structural complexity of CDs, the specific underlying process of their fluorescence is uncertain and yet to be explained. Because of their low toxicity, robust and wide optical absorption, high chemical stability, rapid transfer characteristics, and ease of modification, CDs have been recognized as promising carbon nanomaterials for a variety of sensing applications. Thus, following such outstanding properties of CDs, they have been mixed and imprinted onto different polymeric components to achieve a highly efficient nanocomposite with improved functional groups and properties. Here, in this review, various approaches and techniques for the preparation of polymer/CDs nanocomposites have been elaborated along with the individual characteristics of CDs. CDs/polymer nanocomposites recently have been highly demanded for sensor applications. The insights from this review are detailed sensor applications of polymer/CDs nanocomposites especially for detection of different chemical and biological analytes such as metal ions, small organic molecules, and several contaminants.

Vinyl-functionalized polyphenolic-carbon dot-based fluorometric turn-off-on biosensor for the dual detection of mercury and cysteine and their in vivo sensing in zebrafish larvae

The fluorometric turn-off-on biosensor was developed for the ultra-sensitive detection of mercury (Hg²⁺) and cysteine (Cys) utilizing the highly fluorescent carbon dots (CDs). Herein, the sophisticated low-temperature reflux-mediated reaction was adopted using precursors namely citric acid (CA) and polyphenolic kaempferol (KMP) by using dimethylformamide (DMF) as a solvent. The resulting CDs (i.e., CKCDs) were in the highly negative charged groups (-OH) presented with a bright-orange fluorescence. These CKCDs were functionalized with 4-vinylaniline (4-VA) by employing EDC/NHS coupling reaction, which switched its photoluminescence (PL) towards the strong-blue colored emission and termed as V-CKCDs. The functionalized V-CKCDs can be capable enough to detect mercury via the strong electrostatic interactions between positively charged Hg²⁺ cations and negatively charged anions (-OH groups). Hence, an adequate fluorescence quenching was observed in V-CKCDs with the lowest concentrations of Hg²⁺ around 0.5 μM. Significantly, after adding the complex of V-CKCDs-Hg²⁺ to the Cys, the fluorescence enhancement was observed. This might be attributed from the strong interactions between Hg²⁺ in the fluorescence sensing system and thiol (-SH) moieties from the Cys. The developed V-CKCDs are highly sensitive for detecting Hg²⁺ and Cys, which showed detection limits of 10.6 and 42. 48 nM, respectively. Also, the in vivo studies were investigated in zebrafish larvae using V-CKCDs for the detection of Hg²⁺ and Cys. The V-CKCDs were investigated in the real water samples and human serum to detect Hg²⁺ and Cys, respectively.

Facile fabrication of 17β-estradiol electrochemical sensor using polyaniline/carbon dot-coated glassy carbon electrode with synergistically enhanced electrochemical stability

Previous 17β-estradiol sensors required expensive reagents or complicated fabrication of sensing probes. In this work, a cheap, simple, and reusable electrochemical sensor based on commercially available polyaniline (PANI) and carbon dots (CDs) synthesized from iota-carrageenan was developed for the sensitive detection of 17β-estradiol. The sensor was simply prepared by drop-casting CDs/PANI composite on a glassy carbon electrode (GCE) using poly(vinylidene fluoride) as a binder. With synergistic contributions from both CDs and PANI, the CDs-PANI/GCE was much more electrochemically stable than the CDs/GCE or PANI/GCE. The CDs-PANI/GCE was sensitive to 17β-estradiol across a linear range from 0.001 to 100 μmol L^-1 with a detection limit of 43 nmol L^-1. The electrochemical measurement can be performed in 2 min and the probe can be reused for several hundred times. The CDs-PANI/GCE was selective towards 17β-estradiol against several interferences and gave excellent recovery between 94.4 and 103.7 % from real sample analysis. From intensive investigation on electron transfer process and energy levels, the oxidation reaction of 17β-estradiol occurred on the surface of CDs-PANI/GCE via favorable energy levels and dominantly surface adsorption process through π-π stacking and hydrogen bonding between 17β-estradiol and CDs/PANI. Such unique interfacial interactions also resulted in the synergistically enhanced electrochemical stability of the modified electrode.

Preparation of carbon quantum dots/polyaniline nanocomposite: Towards highly sensitive detection of picric acid

Carbon quantum dots/polyaniline (CQDs/PANI) nanocomposite was successfully prepared by in-situ polymerization of aniline. CQDs were synthesized hydrothermally from gelatin with a diameter size of 4.2 nm and a 17% quantum yield. FTIR, UV-vis absorption, fluorescence spectrophotometer, XRD, TEM, XPS and lifetime decay were used to characterize the obtained nanocomposite. The formation of PANI revealed a high quenching effect on CQDs where the TEM images showed that the formed CQDs were greatly embedded in PANI matrix. In this study, CQDs/PANI nanocomposite was used for the detection of picric acid (PA) in the range 0.37-1.42 μM with a low detection limit (LOD) of 0.056 μM. The prepared sensor showed good enhancement and sensitivity towards PA in comparison to pristine CQDs and other nanostructured materials. The mechanism of PA detection has been studied where it was observed that PA is electrostatically interacted to the nanocomposite through - OH group of PA and the protonated PANI salt formed in CQDs/PANI nanocomposite by fluorescence resonance energy transfer applications. The proposed CQDs/PANI sensor was then utilized in real water samples and successfully determined the different amounts of PA spiked into tap water.

Machine learning algorithms to control concentrations of carbon nanocomplexes in a biological medium via optical absorption spectroscopy: how to choose and what to expect?

A solution of spectroscopic inverse problems, implying determination of target parameters of the research object via analysis of spectra of various origins, is an overly complex task, especially in case of strong variability of the research object. One of the most efficient approaches to solve such tasks is use of machine learning (ML) methods, which consider some unobvious information relevant to the problem that is present in the data. Here, we compare ML approaches to the problem of nanocomplex concentrations determination in human urine via optical absorption spectra, perform preliminary analysis of the data array, find optimal parameters for several of the most popular ML methods, and analyze the results.

Carbon Quantum Dot-Incorporated Chitosan Hydrogel for Selective Sensing of Hg2+ Ions: Synthesis, Characterization, and Density Functional Theory Calculation

A carbon quantum dot-based chitosan hydrogel was prepared in this work as a fluorescence sensor for the selective sensing of Hg2+ ions. Among the eight tested metal ions, the prepared hydrogel exhibited remarkable sensing selectivity and sensitivity toward Hg2+. The results demonstrated that a prominent fluorescence quenching at 450 nm was observed in the presence of Hg2+ with a linear response range of 0-100.0 nM and an estimated limit of detection of 9.07 nM. The as-prepared hydrogel demonstrates pH-dependent fluorescence intensity and sensitivity. The highest fluorescence intensity and sensitivity were obtained under pH 5.0. The excellent sensing selectivity could be attributed to a strong interaction between the hydrogel film and Hg2+ ions to form complexes, which provokes an effective electron transfer for fluorescence quenching. Results from density functional theory (DFT) calculation confirm that the interaction energies (ΔIE) of the hydrogel with three toxic metal ions (Hg2+, Cd2+, and Pb2+) are in the following order: Hg2+ > Cd2+ > Pb2+.

A Review of Off-On Fluorescent Nanoprobes: Mechanisms, Properties, and Applications

With the development of nanomaterials, fluorescent nanoprobes have attracted enormous attention in the fields of chemical sensing, optical materials, and biological detection. In this paper, the advantages of "off-on" fluorescent nanoprobes in disease detection, such as high sensitivity and short response time, are attentively highlighted. The characteristics, sensing mechanisms, and classifications of disease-related target substances, along with applications of these nanoprobes in cancer diagnosis and therapy are summarized systematically. In addition, the prospects of "off-on" fluorescent nanoprobe in disease detection are predicted. In this review, we presented information from all the papers published in the last 5 years discussing "off-on" fluorescent nanoprobes. This review was written in the hopes of being useful to researchers who are interested in further developing fluorescent nanoprobes. The characteristics of these nanoprobes are explained systematically, and data references and supports for biological analysis, clinical drug improvement, and disease detection have been provided appropriately.

A Comparative Study of Top-Down and Bottom-Up Carbon Nanodots and Their Interaction with Mercury Ions

We report a study of carbon dots produced via bottom-up and top-down routes, carried out through a multi-technique approach based on steady-state fluorescence and absorption, time-resolved fluorescence spectroscopy, Raman spectroscopy, infrared spectroscopy, and atomic force microscopy. Our study focuses on a side-to-side comparison of the fundamental structural and optical properties of the two families of fluorescent nanoparticles, and on their interaction pathways with mercury ions, which we use as a probe of surface emissive chromophores. Comparison between the two families of carbon dots, and between carbon dots subjected to different functionalization procedures, readily identifies a few key structural and optical properties apparently common to all types of carbon dots, but also highlights some critical differences in the optical response and in the microscopic mechanism responsible of the fluorescence. The results also provide suggestions on the most likely interaction sites of mercury ions at the surface of carbon dots and reveal details on mercury-induced fluorescence quenching that can be practically exploited to optimize sensing applications of carbon dots.

Carbon Dots for Forensic Applications: A Critical Review

Owing to their superior fluorescence performance, inexpensive synthesis and nontoxic nature, carbon dots (C-dots) are systematically explored in a variety of applications; in this review, we outline and critically discuss recent trends with respect to their potential exploitation in criminal investigation, forensic toxicology and anti-counterfeit interventions. Capitalising on their colour-tuneable behaviour (in the sense that they adopt different colours with respect to the incident radiation), C-dot-based compositions are ideal for the visual enhancement of latent fingerprints, affording improved contrast against multicoloured and patterned backgrounds. As highly sensitive and highly selective optical nanoprobes, C-dots show excellent analytical performance in detecting biological compounds, drugs, explosives, heavy metals and poisonous reactants. In addition, benefiting from their versatile structural and chemical composition, C-dots can be incorporated into ink and polymeric formulations capable of functioning as a new generation of cost-effective barcodes and security nanotags for object authentication and anti-counterfeit applications. Translating these encouraging research outcomes into real-life innovations with significant social and economic impact requires an open, multidisciplinary approach and a close synergy between materials scientists, biologists, forensic investigators and digital engineers.

Development of Biopolymer and Conducting Polymer-Based Optical Sensors for Heavy Metal Ion Detection

Great efforts have been devoted to the invention of environmental sensors as the amount of water pollution has increased in recent decades. Chitosan, cellulose and nanocrystalline cellulose are examples of biopolymers that have been intensively studied due to their potential applications, particularly as sensors. Furthermore, the rapid use of conducting polymer materials as a sensing layer in environmental monitoring has also been developed. Thus, the incorporation of biopolymer and conducting polymer materials with various methods has shown promising potential with sensitively and selectively toward heavy metal ions. In this feature paper, selected recent and updated investigations are reviewed on biopolymer and conducting polymer-based materials in sensors aimed at the detection of heavy metal ions by optical methods. This review intends to provide sufficient evidence of the potential of polymer-based materials as sensing layers, and future outlooks are considered in developing surface plasmon resonance as an excellent and valid sensor for heavy metal ion detection.

Highly Luminescent Ternary Nanocomposite of Polyaniline, Silver Nanoparticles and Graphene Oxide Quantum Dots

Quantum dots (QDs) with photostability show a potential application in optical sensing and biological imaging. In this work, ternary nanocomposite (NC) of high fluorescent polyaniline (PANI)/2-acrylamido-2-methylpropanesulfonic acid (AMPSA) capped silver nanoparticles (NPs)/graphene oxide quantum dots (PANI/Ag (AMPSA)/GO QDs) have been synthesized by in situ chemical oxidative polymerization of aniline in the presence of Ag (AMPSA) NPs and GO QDs. Ag (AMPSA) NPs and GO QDs were prepared by AgNO3 chemical reduction and glucose carbonization methods, respectively. The prepared materials were characterized using UV-visible, Fourier transform infrared (FTIR), photoluminescence and Raman spectroscopies, X-Ray diffractometer (XRD) and high- resolution transmission electron microscopy (HRTEM). HRTEM micrographs confirmed the preparation of GO QDs with an average size of 15 nm and Ag (AMPSA) NPs with an average size of 20 nm. PANI/Ag (AMPSA)/GO QDs NC showed high and stable emission peak at 348 nm. This PANI/Ag (AMPSA)/GO QDs NC can emerge as a new class of fluorescence materials that could be suitable for practical sensing applications.

A morphology-tailored triazine-based crystalline organic polymer for efficient mercury sensing

A melamine-based crystalline organic polymer as a highly efficient ultra-trace Hg²⁺ ion sensor with a detection limit of 0.03 ppb.

Carbon Nanodots: A Review—From the Current Understanding of the Fundamental Photophysics to the Full Control of the Optical Response

Carbon dots (CDs) are an emerging family of nanosystems displaying a range of fascinating properties. Broadly speaking, they can be described as small, surface-functionalized carbonaceous nanoparticles characterized by an intense and tunable fluorescence, a marked sensitivity to the environment and a range of interesting photochemical properties. CDs are currently the subject of very intense research, motivated by their possible applications in many fields, including bioimaging, solar energy harvesting, nanosensing, light-emitting devices and photocatalyis. This review covers the latest advancements in the field of CDs, with a focus on the fundamental understanding of their key photophysical behaviour, which is still very debated. The photoluminescence mechanism, the origin of their peculiar fluorescence tunability, and their photo-chemical interactions with coupled systems are discussed in light of the latest developments in the field, such as the most recent results obtained by femtosecond time-resolved experiments, which have led to important steps forward in the fundamental understanding of CDs. The optical response of CDs appears to stem from a very complex interplay between the electronic states related to the core structure and those introduced by surface functionalization. In addition, the structure of CD energy levels and the electronic dynamics triggered by photo-excitation finely depend on the microscopic structure of any specific sub-type of CD. On the other hand, this remarkable variability makes CDs extremely versatile, a key benefit in view of their very wide range of applications.

A novel ferrocenyl–naphthalimide as a multichannel probe for the detection of Cu(ii) and Hg(ii) in aqueous media and living cells

The first reported probe that has been used for the bifunctional fluorescent monitoring Cu²⁺ and Hg²⁺ ions in living cells.

Graphitic carbon nitride supported platinum nanocomposites for rapid and sensitive colorimetric detection of mercury ions

In this study, graphitic carbon nitride supported platinum nanocomposites (g-C₃N₄/PtNPs) have been synthesized for the first time by an ultrasonic-assisted chemical reduction method. By using g-C₃N₄ as the stabilizer, Pt ions could be reduced to PtNPs by NaBH₄ and uniformly deposited on the surface of g-C₃N₄. The resulting g-C₃N₄/PtNPs exhibited enhanced catalytic activity for the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) compared to that of g-C₃N₄ or PtNPs alone. After interaction with Hg²⁺, the catalytic activity of g-C₃N₄/PtNPs was effectively inhibited due to the formation of HgPt amalgam. On the basis of this effect, a novel label free colorimetric sensor has been developed for sensitive detection of Hg²⁺ through the g-C₃N₄/PtNPs mediated catalytic reaction. A detection limit as low as 1.23 nM was achieved. This assay also exhibited excellent selectivity toward Hg²⁺ over other metal ions. In addition, it was successfully applied to the determination of Hg²⁺ in real water samples. In view of the advantages, such as simple operation, cost-effective, rapid response and naked-eye observation, the developed colorimetric sensor hold great potential for the detection of toxic Hg²⁺ in environmental and biological samples.

Fabrication of valine-functionalized graphene quantum dots and its use as a novel optical probe for sensitive and selective detection of Hg2

The functionalization of graphene quantum dots has become a powerful method to modulate its chemical, electronic and optical properties for various applications. In the study, we reported a facile synthesis of valine-functionalized graphene quantum dots (Val-GQDs) and its use as a novel fluorescent probe for optical detection of Hg²⁺. Herein, Val-GQDs was synthesized by the thermal pyrolysis of citric acid and valine. The resulting Val-GQDs has an average size of 3nm and the edge of graphene sheets contains the rich of hydrophilic groups, leading to a high water-solubility. Compared to the GQDs prepared by thermal pyrolysis of citric acid, Val-GQDs exhibits a stronger fluorescence (>10-fold) and better photostability (>4-fold). Interestingly, the existence of valine moieties in the Val-GQDs results in a more sensitive fluorescent response to Hg²⁺. The fluorescent signal will linearly decrease with the increase of Hg²⁺ concentration in the range from 0.8nM to 1μM with the correlation coefficient of 0.992. The detection limit is 0.4nM (S/N=3), which the sensitivity is >14-fold that of GQDs. The analytical method provides the prominent advantage of sensitivity, selectivity and stability. It has been successfully applied in the optical detection of Hg²⁺ in real water samples. The study also provides a promising approach for the design and synthesis of functionalized GQDs to meet the needs of further applications in sensing and catalysis.

Protein self-assembly onto nanodots leads to formation of conductive bio-based hybrids

The next generation of nanowires that could advance the integration of functional nanosystems into synthetic applications from photocatalysis to optical devices need to demonstrate increased ability to promote electron transfer at their interfaces while ensuring optimum quantum confinement. Herein we used the biological recognition and the self-assembly properties of tubulin, a protein involved in building the filaments of cellular microtubules, to create stable, free standing and conductive sulfur-doped carbon nanodots-based conductive bio-hybrids. The physical and chemical properties (e.g., composition, morphology, diameter etc.) of such user-synthesized hybrids were investigated using atomic and spectroscopic techniques, while the electron transfer rate was estimated using peak currents formed during voltammetry scanning. Our results demonstrate the ability to create individually hybrid nanowires capable to reduce energy losses; such hybrids could possibly be used in the future for the advancement and implementation into nanometer-scale functional devices.

Rapamycin/DiR loaded lipid-polyaniline nanoparticles for dual-modal imaging guided enhanced photothermal and antiangiogenic combination therapy

Imaging-guided photothermal therapy (PTT) has promising application for treating tumors. Nevertheless, so far imaging-guided photothermal drug-delivery systems have been developed with limited success for tumor chemo-photothermal therapy. In this study, as the proof-of-concept, a stimuli-responsive tumor-targeting rapamycin/DiR loaded lipid-polyaniline nanoparticle (RDLPNP) for dual-modal imaging-guided enhanced PTT efficacy is reported for the first time. In this system, polyaniline (PANI) with π-π electronic conjugated system and effective photothermal efficiency is chosen as the appropriate model receptor of fluorescence resonance energy transfer (FRET), and loaded cyanine probe (e.g., 1,1-dioctadecyl-3,3,3,3-tetramethylindotricarbocyanine iodide, DiR) acts as the donor of near-infrared fluorescence (NIRF). In addition, rapamycin (RAPA), which is used as the antiangiogenesis chemotherapeutic drug, can cutdown the tumor vessels and delay tumor growth obviously. After intravenous treatment of RDLPNPs into Hela tumor bearing mice, fluorescent (from DiR) and enhanced photoacoustic (from DLPNPs) signals were found in tumor site over time, which reached to peak at the 6h time point. After irradiating with an NIR laser, a good anti-tumor effect was observed owing to the enhanced photothermal and antiangiogenic effect of RDLPNPs. These results show that the multifunctional nanoparticle can be used as a promising imaging-guided photothermal drug delivery nanoplatform for cancer therapy.

Fluorescent probes for "off-on" highly sensitive detection of Hg²⁺ and L-cysteine based on nitrogen-doped carbon dots

Fluorescent nitrogen-doped carbon dots (NCDs) were synthesized by a facile, and low-cost one-step hydrothermal strategy using citric acid as carbon source and ammonia solution as nitrogen source for the first time. The obtained NCDs show stable blue fluorescence with a high quantum yield of 35.4%, along with the fluorescence lifetime of ca. 6.75 ns. Most importantly, Hg(2+) can completely quench the fluorescence of NCDs as a result of the formation of a non-fluorescent stable NCDs-Hg(2+) complex. Static fluorescence quenching towards Hg(2+) is proved by the Stern-Volmer equation, ultraviolet-visible absorption spectra, temperature dependent quenching and fluorescence lifetime measurements. Subsequently, the fluorescence of the NCDs-Hg(2+) system is completely recovered with the addition L-cysteine (L-Cys) owing to the dissociation of NCDs-Hg(2+) complex to form a more stable Hg(2+)-L-Cys complex by Hg(2+)-S bonding. Therefore, such NCDs can be used as an effective fluorescent "turn-off" probe for rapid, rather highly selective and sensitive detection of Hg(2+), with a limit of detection (LOD) as low as 1.48 nM and a linear detection range of 0-10 μM. Interestingly, NCDs-Hg(2+) system can be conveniently employed as a fluorescent "turn-on" sensor for highly selective and sensitive detection of L-Cys with a low LOD of 0.79 nM and a wide linear detection range of 0-50 μM. Further, the sensitivity of NCDs to Hg(2+) is preserved in tap water with a LOD of 1.65 nM and a linear detection range of 0-10 μM.

Facile synthesis of fluorescent polyaniline microspheres and their use for the detection of mercury ions

Bright blue fluorescent polyaniline microspheres were prepared by a simple controlled oxidation under mild conditions. A simple, highly sensitive fluorometric Hg²⁺ probe has been constructed.