Nitrogen-doped carbon nanoparticle modulated turn-on fluorescent probes for histidine detection and its imaging in living cells

Boronic Acid-Decorated Carbon Dot-Based Semiselective Multichannel Sensor Array for Cytokine Discrimination and Oral Cancer Diagnosis

Cytokines are essential components of the immune system and are recognized as significant biomarkers. However, detection of a single cytokine is not precise and reliable enough to satisfy the requirements for diagnosis. Herein, we developed a pattern recognition-based method for the multiplexed sensing of cytokines, which involves three-color-emitting boronic acid-decorated carbon dots (BCDs) and arginine-modified titanium carbide (Ti3C2 MXenes) as the sensor array. Initially, the fluorescence signals of the three BCDs were quenched by Ti3C2 MXenes. In the presence of cytokines, the fluorescence intensity of the BCDs was restored or further quenched by different cytokines. The fluorescence response occurs in two steps: first, boronic acid interacts with cis-diol functional groups of cytokines, and second, arginine headgroup selectively interacts with glycans. By exploiting the different competing binding of the BCDs and the cytokines toward Ti3C2 MXenes, seven cytokines and their mixtures can be effectively discriminated at a concentration of 20 ng mL-1. Furthermore, our sensor array demonstrated an excellent performance in classifying human oral cancer saliva samples from healthy individuals with clinically relevant specificity. The noninvasive method offers a rapid approach to cytokine analysis, benefiting early and timely clinical diagnosis and treatment.

Construction of a Dual-Mode Biosensor with Ferrocene as Both a Signal Enhancer and a Signal Tracer for Electrochemiluminescent and Electrochemical Enantioselective Recognition

We demonstrate for the first time the construction of a dual-mode biosensor for electrochemiluminescent (ECL) and electrochemical chiral recognition of l- and d-isomers of amino acids, with ferrocene (Fc) as both a signal enhancer and a signal tracer. With the dissolved oxygen as a coreactant, ZnIn2S4 acts as the ECL emitter to generate a weak cathodic ECL signal. Fc can enter into the β-cyclodextrin (β-CD) cavity on ZnIn2S4-modified electrode as a result of host-guest interaction. Since Fc can promote H2O and O2 to produce abundant reactive oxygen species (ROS) (e.g., O2·- and ·OH), the ECL signal of ZnIn2S4 can be further amplified with Fc as a coreaction accelerator. Meanwhile, Fc molecules on the β-CD/ZnIn2S4-modified electrode can be electrochemically oxidized to Fc+ to produce a remarkable oxidation peak current. When l-histidine (l-His) is present, the matching of the l-His configuration with the β-CD cavity leads to the entrance of more l-His into the cavity of β-CD than d-histidine (d-His), and the subsequent competence of l-His with Fc on the Fc/β-CD/ZnIn2S4-modified electrode induces the decrease in both Fc peak current and ZnIn2S4-induced ECL intensity. This dual-mode biosensor can efficiently discriminate l-His from d-His, and it can sensitively monitor l-His with a detection limit of 7.60 pM for ECL mode and 3.70 pM for electrochemical mode. Moreover, this dual-mode biosensor can selectively discriminate l-His from other l- and d-isomers (e.g., threonine, phenylalanine, and glutamic acid), with potential applications in the chiral recognition of nonelectroactive chiral compounds, bioanalysis, and disease diagnosis.

Dual-emission fluorescence detection of histidine using carbon dots and calcein/Ni2+ complexes

Histidine (His) is a natural amino acid that plays very important roles in biota. However, the low concentrations of His in biological fluids and the similar structures and properties of other amino acids mean it is difficult to selectively determine His concentrations in biological fluids with a high degree of sensitivity. A novel ratiometric fluorescence probe for detecting His in aqueous solutions is described here. The method involves carbon dots (CDs) and calcein/Ni²⁺ complexes. At an excitation wavelength of 480 nm, the CD/calcein system emits green fluorescence (maximum emission from calcein at 512 nm) and red fluorescence (maximum emission from CDs at 617 nm). The presence of Ni²⁺ decreases the calcein fluorescence intensity because of static quenching caused by the formation of calcein/Ni²⁺ complexes but the CD fluorescence intensity remains almost unchanged. Fluorescence of calcein/Ni²⁺ complexes provides the response, and the presence of His binds to Ni²⁺ via cooperative chelation and produces free calcein causing fluorescence to be recovered. CDs provide a self-calibration fluorescence signal, the intensity of which remains almost unchanged in the presence of His. The ratio of the fluorescence intensities at 512 and 617 nm (I₅₁₂/I₆₁₇) was strongly related to the His concentration in the range 0.5-22 μM, and the detection limit was 0.16 μM. The specificity of Ni²⁺/His interactions allows His to be determined without interference from other species. The method was successfully used to determine His in diluted human urine. The recovery was acceptable, suggesting that the biosensor can be used to determine His in real samples.

Injectable Dual-Dynamic-Bond Cross-Linked Hydrogel for Highly Efficient Infected Diabetic Wound Healing

Diabetic wound is a significant challenge for clinical treatment with high morbidity and mortality. Plenty of hydrogels with good biocompatibility have been widely used in diabetic wound healing. However, most of them cannot be directly absorbed and utilized by the wounds, which prolongs the regeneration time. Here a new type of healing hydrogel is developed that is based on histidine, a natural dietary essential amino acid that is significant for tissue formation. The amino acid is cross-linked with zinc ions (Zn²⁺ ) and sodium alginate (SA) via dynamic coordinate and hydrogen bonds, respectively, forming a histidine-SA-Zn²⁺ (HSZH) hydrogel with good injectable, adhesive, biocompatible, and antibacterial properties. Application of this dual-dynamic-bond cross-linked HSZH hydrogel accelerates the migration and angiogenesis of skin-related cells in vitro. Furthermore, it significantly promotes the healing of infected diabetic wounds in vivo and uniquely allows a full repair of wounds within ≈13 days, while ≈27 days are required for the healing process of the control group. This work provides a new strategy for designing wound dressing materials, that weakly cross-linked material based on tissue-friendly micromolecules can heal the wounds more efficiently than highly cross-linked materials based on long-chain polymers.

Green synthesis of fluorescent carbon nanospheres from chrysanthemum as a multifunctional sensor for permanganate, Hg(II), and captopril

A simple and green method for the synthesis of fluorescent carbon nanospheres (CNs) was proposed using chrysanthemum as a natural precursor and ethylenediamine as the co-reagent. The prepared CNs show strong blue fluorescence in water with quantum yield of 13.7 %, and distinguished fluorescent stability against photobleaching and ion strength. Meanwhile, the fluorescence signal of CNs is reversible and sensitive to temperature in the range of 20-80 °C, which makes CNs useful as a temperature sensor. More importantly, the CNs can serve as excellent fluorescent sensors for detecting MnO₄^- and Hg²⁺ with the detection limit of 0.72 and 0.26 μM, respectively. MnO₄^- quenches the fluorescence of CNs through inner filter effect and static quenching mechanism, while Hg²⁺ forms a stable complex with the amino group on the surface of CNs, resulting in the fluorescence quenching of CNs. However, the stronger affinity between Hg²⁺ and captopril (Cap) results in the fluorescence quenched by Hg²⁺ recovery after the addition of Cap. Thus, the CNs-Hg²⁺ system is employed as a novel sensitive and selective fluorescence "turn-on" sensor for Cap in the range of 0-75 μM. Inspired by the sensing results, the developed sensors were successfully used for the determination of MnO₄^-, Hg²⁺ in river water samples and Cap in the pharmaceutical and urine samples.

Fluorimetric and ratiometric colorimetric dual-mode detection of organophosphorus pesticides based on carbon dots/DTNB

Carbon dots/DTNB as fluorimetric and ratiometric colorimetric dual-mode probes for the detection of chlorpyrifos.

A Convenient and Label-Free Colorimetric Detection for L-Histidine Based on Inhibition of Oxidation of 3,3',5,5'-Tetramethylbenzidine-H2O2 System Triggered by Copper Ions

L-Histidine (L-His) is an essential amino acid, which is used to synthesize proteins and enzymes. The concentration of L-His in the body is controlled to regulate tissue growth and repair of tissues. In this study, a rapid and sensitive method was developed for colorimetric L-his detection using Cu²⁺ ions to inhibit the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB)-H₂O₂ system. H₂O₂ can oxidize TMB to oxTMB in the presence of copper, and the change in color from colorless (TMB) to blue (oxTMB) is similar to that observed in the presence of peroxidase. However, because the imidazole ring and carboxyl group of L-His can coordinate with Cu²⁺ ions to form stable L-His-Cu²⁺ complexes, the color of the TMB-H₂O₂ solution remains unchanged after the addition of L-His. Therefore, because L-His effectively hinders the colorimetric reaction of TMB with H₂O₂, this assay can be used to quantitatively determine the concentration of L-His in samples. Under optimized conditions, our colorimetric sensor exhibited two linear ranges of 60 nM to 1 μM and 1 μM to 1 mM for L-His detection and a detection limit of 50 nM (S/N = 3); furthermore, the assay can be performed within 20 min. Moreover, the proposed assay was used to determine the concentration of L-His in urine samples, suggesting that this convenient and label-free colorimetric method presents promising applications in bioanalytical chemistry and clinical diagnosis.

Fluorescent nitrogen-doped carbon dots for high selective detecting p-nitrophenol through FRET mechanism

A facile, friendly and one-step hydrothermal protocol was used to synthesize nitrogen-doped carbon dots (N-CDs) by utilizing hexamethylenetetramine and ethanediamine as the carbon and nitrogen sources. It demonstrated good water solubility and fluorescence properties were stable, whether in acidic or alkaline. Quantum yield (QY) of N-CDs was 8.3% at an excitation wavelength of 325 nm with maximum emission at 425 nm. The fluorescence of N-CDs achieved very high fluorescence quenching of 60% in the detection of p-nitrophenol (p-NP) in aqueous medium via fluorescence resonance energy transfer (FRET) mechanisms. Under optimum conditions, fluorescence probs of N-CDs had strong selectivity to p-NP, and the fluorescence intensity was linearly proportional to p-NP concentration from 0.5 to 70.0 μM with a detection limit of 0.201 μM. The corresponding cell experiments were also performed, indicating that the prepared N-CDs possessed low cytotoxicity and good biocompatibility. Meanwhile, the N-CDs can be used for the determination of p-NP in river water and industrial wastewater.

Ratiometric detection of p-nitrophenol and its derivatives using a dual-emissive neuron cell-like carbonized probe based on a ππ stacking quenching mechanism

p-Nitrophenol and its derivatives can cause serious harm to the health of mankind and the earth's ecosystem. Therefore, it is necessary to develop a novel and rapid detection technology for p-nitrophenol and its derivative. Herein, excellent water-soluble, large-size and dual-emissive neuron cell-analogous carbon-based probes (NCNPs) have been prepared via a solvothermal approach, using o-phenylenediamine as the only precursor, which exhibit two distinctive fluorescence (FL) peaks at 420 and 555 nm under 345 nm excitation. The NCNPs show a neuron cell-like branched structure, are cross-connected, and are in the range of 10-20 nm in skeleton diameter. Interestingly, their blue-green dual-colour fluorescence is quenched by p-nitrophenol or its derivative due to the specific mechanism of the ππ stacking interactions or internal filtration effect. Accordingly, a simple, rapid, direct and free-label ratiometric FL detection of p-nitrophenol is proposed. An excellent linear relationship shows linear regions over the range of 0.1-50 μM between the ratio of the FL intensity (FL555 nm/FL420 nm) and the concentrations of p-nitrophenol. The detection limit is as low as 43 nM (3σ). Importantly, the NCNP-based probe also shows acceptable repeatability and reproducibility for the detection of p-nitrophenol and its derivatives, and the recovery results for p-nitrophenol in real wastewater samples are favourable.

Multifunctional N-Doped Carbon Dots for Bimodal Detection of Bilirubin and Vitamin B12, Living Cell Imaging, and Fluorescent Ink

A N-doped carbon dot (NCD) has been synthesized via a simplistic one-step hydrothermal technique using l-aspartic acid and 3,6-diaminoacridine hydrochloride. The NCDs exhibit a high quantum yield (22.7%) and excellent optical stability in aqueous media. Additionally, NCDs display good solid-state yellowish-green emission and are suitable for security ink applications. The remarkable fluorescence (FL) properties of NCDs are further applied to develop a multifunctional sensor for bilirubin (BR) and vitamin B₁₂ (VB12) via fluorescence quenching. We have systematically studied the FL quenching mechanisms of the two analytes. The primary quenching mechanism of BR is via the Förster resonant energy transfer (FRET) pathway facilitated by the H-bonding network between the hydrophilic moieties existing at the surface of BR and NCDs. In contrast, the inner filter effect (IFE) is mainly responsible for the recognition of VB12. The practicability of the nanoprobe NCDs is further tested in real-sample analysis for BR (human serum and urine samples) and VB12 (VB12 tablets, human serum, and energy drink) with a satisfactory outcome. The in vitro competency is also verified in the human cervical cancer cell line (HeLa cell) with negligible cytotoxicity and significant biocompatibility. This result facilitates the application of NCDs for bioimaging and recognition of VB12 in a living organism.

Development of an ultrasensitive spectrophotometric method for carmine determination based on fluorescent carbon dots

A high-efficiency spectrophotometric method based on nitrogen-doped fluorescent carbon dots (N-FCDs) was developed for the ultrasensitive determination of carmine (CRM) in foodstuffs. The N-FCDs were fabricated via a one-pot hydrothermal method with m-phenylenediamine as the starting material. The detection principle was based on the fluorescence quenching effect of N-FCDs by CRM, where their interaction was due to the inner filter effect (IFE) and static quenching. A good linear relationship was established for CRM detection in a concentration range of 0.1-10.0 μM with a detection limit as low as 11.2 nM. The proposed method achieved satisfactory results for CRM determination in commercial food products with recoveries better than 98.6% and relative standard deviations (RSDs) less than 4.07%. The method established in this study was simple, ultrasensitive and reliable for rapid detecting CRM in a food matrix, which could be potentially used as a useful sensing agent for the analysis of additive food colourants.

Limitation-induced fluorescence enhancement of carbon nanoparticles and their application for glucose detection

Rational design of detection strategy is the key to high-performance fluorescence analysis. In this article, we found that the glucose-induced limitations can greatly enhance the fluorescence of functionalized carbon nanoparticles (CNPs), which are synthesized through one-step thermal pyrolysis method using phenylboronic acid derivative as the precursors. The glucose can assembly onto the surface of the CNPs to form a "shell", limiting the surfaces' intramolecular rotation and reducing non-radiative decay, which hence resulted in enhanced fluorescence of the CNPs. Under optimal conditions, the fluorescence intensity of the CNPs is nearly 70-fold enhanced, and the method has low detection limit (10 μM) and linear response in the concentration range from 50 μM to 2000 μM. Based on this interesting "target-triggered limitation-induced fluorescence enhancement" phenomenon, a simple and effective non-enzymatic fluorescence enhancement method was developed and successfully applied to the determination of glucose in spiked serum samples. This work provides new insight into the design of fluorescence-enhanced detection strategies based on the limitation-induced property.

Yellow emission carbon dots for highly selective and sensitive OFF-ON sensing of ferric and pyrophosphate ions in living cells

A simple "OFF-ON" fluorescent system was proposed for selective and sensitive detection of ferric ion (Fe³⁺) and pyrophosphate (PPi) in living cells. The method was constructed based on the bright yellow emission of carbon dots (y-CDs), which were prepared using o-phenylenediamine (OPD) as the precursor via a facile hydrothermal treatment. The as-obtained y-CDs, with an average size of 2.6 nm, exhibited an excitation-independent emission peak at 574 nm. The fluorescence of y-CDs can be remarkably quenched by Fe³⁺ with high selectivity and sensitivity. Interestingly, the quenched fluorescence can be recovered regularly upon addition of PPi, showing a promising detection for PPi. The linear ranges for Fe³⁺ and PPi detections were 0.05-80 and 0.5-120 μM, respectively, and the corresponding limit of detections (LODs) were 22.1 and 73.9 nM. As we proved the y-CDs have negligible cytotoxicity and excellent biocompatibility, further application to the fluorescence imaging of intracellular Fe³⁺ and PPi were conducted, suggesting the prepared y-CDs can be used to monitor Fe³⁺ and PPi variation in living cells. Overall, our developed y-CDs-based OFF-ON switch fluorescent probe has the advantages of simplicity, agility, high sensitivity and selectivity, which provides a promising platform for environmental and biology applications, and paves a new avenue for monitoring the hydrolysis process of adenosine triphosphate disodium salt (ATP) by detection of PPi in organisms.

Titanium carbide MXenes combined with red-emitting carbon dots as a unique turn-on fluorescent nanosensor for label-free determination of glucose

Titanium carbides (Ti3C2), a new family of two-dimensional (2D) nanomaterials, have attracted extensive attention due to their unique structure and desirable physiochemical properties. Herein, we developed an effective and selective fluorescent turn-on nanosensor for glucose detection based on Ti3C2 nanosheets combined with red-emitting carbon dots (RCDs). The fluorescence intensity of RCDs could be effectively quenched (>96%) by Ti3C2 nanosheets through the inner-filter effect (IFE). In the presence of H2O2, the quenched fluorescence of the RCDs can remarkably recover due to the Ti3C2 nanosheets which were oxidized into Ti(OH)4 by H2O2. Based on H2O2 generated from oxidation of glucose catalyzed by glucose oxidase, the nanosensor can also be exploited for monitoring glucose. Under optimal conditions, a linear relationship between the increased fluorescence intensity of RCDs and the concentration of glucose was established in the range from 0.1 to 20 mM. The detection limit was 50 μM (S/N = 3). The proposed nanosensor also represented excellent selectivity for glucose analysis in biological fluid samples, providing a valuable platform for glucose sensing in clinical diagnostics.

Ratiometric assay of mercury ion based on nitrogen-doped carbon dots with two different optical signals: second-order scattering and fluorescence

Ratiometric assays, which can effectively surmount external interference, have attracted extensive research interests. Herein, a novel ratiometric sensing platform for Hg²⁺ is designed based on nitrogen-doped carbon dots (N-CDs) with two different optical signals. Under a single excitation, N-CDs have two emission peaks around 668 nm and 412 nm, which are second-order scattering and fluorescence, respectively. Upon the addition of Hg²⁺, the weak scattering emission at 668 nm can be increased apparently, while the strong fluorescence intensity at 412 nm is weakened. Moreover, the ratio of scattering intensity to fluorescence intensity is linearly dependent on Hg²⁺ concentration (0.1-10 μM and 10-30 μM, respectively), and the detection limit is 66 nM. In addition, the ratiometric sensing mechanism is investigated in detail, which is due to the combined effect of aggregation-induced fluorescence quenching and scattering enhancement. Furthermore, the developed sensing approach holds a promising application for Hg²⁺ detection in actual samples. Graphical abstract.

Eco-Friendly Sustainable Fluorescent Carbon Dots for the Adsorption of Heavy Metal Ions in Aqueous Environment

The materials and substances required for sustainable water treatment by adsorption technique, are still being researched widely by distinguished classes of researchers. Thus, the need to synthesize substances that can effectively clean up pollutants from the environment cannot be overemphasized. So far, materials in bulk forms that are rich in carbon, such as biochar and varieties of activated carbon have been used for various adsorptive purposes. The use of bulk materials for such purposes are not efficient due to minimal surface areas available for adsorption. This study explores the adsorption task at nano dimension using carbon dots (CDs) from tapioca. The properties of carbon structure and its influence on the adsorptive efficacy of carbon nanoparticles were investigated by energy-dispersive spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR), high resolution transmission electron microscopy (HrTEM), and atomic force microscopy (AFM). The results implied carbon present in CDs are good adsorbents for effective adsorption of heavy metal ions (lead) with removal efficiency of 80.6% in aqueous environment. The adsorption process as explored by both Langmuir and Freundlich isotherms have proven favorability of the adsorption process. Langmuir form two and three have correlation coefficients R2 at 0.9922 and 0.9912, respectively. The Freundlich isotherm confirms CDs as having defined surface heterogeneity and the exponential distribution of active sites. The adsorption of lead unto CDs obeyed the second order kinetic model with coefficient of determination, R2 of 0.9668 and 0.9996 at an initial lead concentration of 20 mg/L and 100 mg/L, respectively. The findings validated the efficiency of CDs derived from tapioca as an excellent material for further utilization in the environmental fields of wastewater pollution detection and clean up, bio-imaging, and chemical sensing applications.

Antioxidant Activity of Graphene Quantum Dots Prepared in Different Electrolyte Environments

Antioxidants can reduce or inhibit damage such as oxidative decay caused by elevated levels of free radicals. Therefore, pursuing antioxidants with excellent properties has attracted more and more attention. Graphene quantum dots (GQDs) are considered a promising material because of their good free radical scavenging activity, low toxicity, and excellent water solubility. However, their scavenging efficiency, antioxidant mechanism, and effective control methods need to be improved. Herein, in order to further reveal the antioxidant mechanism of GQDs, the role of electrolytes in improving the antioxidant activity of GQDs is explored. In addition, 1,1-diphenyl-2-picrazine (DPPH∙), hydroxyl (∙OH), and superoxide (∙O₂⁻) free radicals are used to evaluate the antioxidant activity of the as-prepared GQDs. Combined with transmission electron microscopy, Fourier-transform infrared spectroscopy, Raman spectroscopy, and cyclic volt–ampere characteristic curves, the effects of an electrolytic environment on the surface functional groups, charge transfer capability, and defect states of GQDs are obtained. The antioxidant mechanism of GQDs and how to improve their antioxidant activity are further elucidated.

A fluorescent molecularly imprinted device for the on-line analysis of AFP in human serum

MIT is a promising strategy in antibody free analysis for tumour markers. Conventional nanosized MIPs with off-line analysis are beset by tedious operation and unsatisfactory analysis performance. In this work, an on-line analytical device to directly detect AFP, which is a typical tumour marker in cancer screening, was prepared for the first time. A microscope slide was chosen to be the basis of the device. APBA-PA, a polymerizable fluorescent boronic acid monomer, was synthesised and grafted on the surface of the microscope slide to act as the signal transduction pathway between the templates and the device. Along with the hydrolysis of TEOS and the elution of the templates, a portable, stable, easy to operate and low-cost analysis device for AFP with excellent repeatability was successfully prepared. Owing to the excellent selectivity and highly sensitive fluorescence response ability of the device towards the templates, the on-line detection of AFP in human serum was realized. A series of characterizations were applied to the device, and its analysis performance and possible detection mechanism were carefully studied. Furthermore, the device exhibited appropriate application prospects by comparing its analysis results with those of the commercially available ELISA. In our perception, this work is an important step towards MIPs for clinical applications.

P,N Codoped carbon dots as an efficient "off-on" fluorescent probe for lipoic acid detection and its cellular dual-color imaging

A facile single hydrothermal method was developed to synthetize P,N codoped carbon dots (P,N/CDs), which show strong and stable fluorescence, good water solubility, low toxicity and good biocompatibility. Hence, a novel and efficient "off-on" P,N/CDs fluorescent probe was developed for the highly sensitive detection of lipoic acid (LA) for the first time. The fluorescence of the P,N/CDs was quenched by Cu²⁺ forming a P,N/CDs-Cu²⁺ complex, which acted as the "off" process, but Cu²⁺ could be removed by LA, due to stronger chelating between LA and Cu²⁺, forming a more stable complex, which recovered the fluorescence of the P,N/CDs, in order to achieve the "on" process. Under optimal conditions, the concentration of LA and the increased fluorescence intensity of the P,N/CDs-Cu²⁺ complex displayed a good linear relationship within the range of 0.05-28 μM, with a detection limit (S/N = 3) of 0.02 μM. The established "off-on" fluorescent probe was successfully applied to the analysis of LA in urine samples. The average recoveries were in the range of 98.3-101.5%, with a relative standard deviations of less than 3.1%. In addition, the P,N/CDs were also successfully applied to cellular dual-color imaging of live T24 cells. The results show that the P,N/CDs have great application potential in clinical diagnosis, bioassay and bioimaging. Graphical abstract.

A novel label-free fluorescent detection of histidine based upon Cu2+-specific DNAzyme and hybridization chain reaction

A novel label-free fluorescent sensor for histidine was developed based upon Cu²⁺-specific DNAzyme, hybridization chain reaction(HCR) and triplex DNA. Cu²⁺ can bind to the histidine, in the presence of histidine, leading to the inhibition of the cleavage of substrate strand of Cu²⁺-dependent DNAzyme, then the intact substrate strand trigger the HCR between H1 and H2. The HCR product can be recognized by triplex-forming oligonucleotide (TFO) through triplex formation and reported by the fluorescence of berberine, the fluorescence intensity of the sensing system was proportional to the concentration of histidine during the range of 5.7-455 nmol L^-1, with a detection limit of 2.0 nmol L^-1.

pH-Dependent photoluminescence “switch-on” nanosensors composed of silver nanoparticles and nitrogen and sulphur co-doped carbon dots for discriminative detection of biothiols

A nanomaterial surface energy transfer (NSET) system composed of silver nanoparticles (AgNPs) and nitrogen and sulphur co-doped carbon dots (N,S-CDs) was established to discriminate biothiols, featuring the pH-promoted distinct PL “switch-on” response.

Highly selective and reproducible electroanalysis for histidine in blood with turn-on responses at a potential approaching zero using tetrahedral copper metal organic frameworks

Tetrahedral copper metal organic frameworks were fabricated for the electroanalysis of histidine with turn-on responses at a potential approaching zero.

A review on nanostructured carbon quantum dots and their applications in biotechnology, sensors, and chemiluminescence

Carbon quantum dots (CQDs) are a member of carbon nanostructures family which have received increasing attention for their photoluminescence (PL), physical and chemical stability and low toxicity. The classical semiconductor quantum dots (QDs) are semiconductor particles that are able to emit fluorescence by excitation. The CQDs is mainly referred to photoluminescent carbon nanoparticles less than 10 nm, with surface modification or functionalization. Contrary to other carbon nanostructures, CQDs can be synthesized and functionalized fast and easily. The fluorescence origin of the CQDs is a controversial issue which depends on carbon source, experimental conditions, and functional groups. However, PL emissions originated from conjugated π-domains and surface defects have been proposed for the PL emission mechanisms of the CQDs. These nanostructures have been used as nontoxic alternatives to the classical heavy metals containing semiconductor QDs in some applications such as in-vivo and in-vitro bio-imaging, drug delivery, photosensors, chemiluminescence (CL), and etc. This paper will introduce CQDs, their structure, and PL characteristics. Recent advances of the application of CQDs in biotechnology, sensors, and CL is comprehensively discussed.

Bright Yellow Fluorescent Carbon Dots as a Multifunctional Sensing Platform for the Label-Free Detection of Fluoroquinolones and Histidine

Owing to their diverse properties, fluorescent carbon dots (CDs) have attracted more attention and present enormous potential in development of sensors, bioimaging, drug delivery, microfluidics, photodynamic therapy, light emitting diode, and so forth. Herein, a multifunctional sensing platform based on bright yellow fluorescent CDs (Y-CDs) was designed for the label-free detection of fluoroquinolones (FQs) and histidine (His). The Y-CDs with superior optical and biological merits including high chemical stability, good biocompatibility, and low cytotoxicity were simply synthesized via one-step hydrothermal treatment of o-phenylenediamine ( o-PD) and 4-aminobutyric acid (GABA). The Y-CDs can be utilized to directly monitor the amount of FQs based on fluorescence static quenching owing to the specific interaction between FQs and Y-CDs. Then, the fluorescence of this system can be effectively recovered upon addition of His. The multifunctional sensing platform exhibited high sensitivity and selectivity toward three kinds of FQs and His with low detection limits of 17-67 and 35 nM, respectively. Benefiting from these outstanding characters, the Y-CDs were successfully employed for trace detection of FQs in real samples such as antibiotic tablets and milk products. Furthermore, the probe was also extended to cellular imaging. All of the above prove that this multifunctional sensing platform presents great prospect in multiple applications such as biosensing, biomedicine, disease diagnosis, and environmental monitoring.

Rational design of an "on-off-on" fluorescent switch for Cu2+ and histidine based on chiral macrocyclic dioxopolyamine

A novel chemosensor 1 having a chiral macrocyclic dioxopolyamine of C₂ symmetry as a receptor and anthracene as a signal unit has been designed and synthesized for cations and α-amino acids recognition in DMSO-HEPES buffer (1:9, v/v, pH 7.2). The ligand exhibited selective response to Cu²⁺ even in the presence of other metal ions with a fluorescence "switch-off" behavior. Additionally, the in situ generated 1-Cu²⁺ ensemble displayed specific recognition to histidine by a "switch-on" fluorescence response. For this dual functional switch, its sensing behavior via a displacement mode was confirmed by ¹H NMR titration and ESI mass spectroscopy. Sequential "on-off-on" fluorescence responses of 1 to Cu²⁺ and histidine are successfully applied in HeLa cells.

Nitrogen-doped carbon dots with excitation-independent long-wavelength emission produced by a room-temperature reaction

Nitrogen-doped carbon dots (CDs) have been produced by a new facile "bottom-up" synthesis, using the room-temperature reaction between acetonitrile and sodium-naphthalene. The obtained hydrophobic CDs are monodisperse (∼2.6 nm) and present an excitation-independent emission at ∼588 nm with a small full width at half-maximum (FWHM) of ∼52 nm. The CDs can be simply modified to be hydrosoluble and have been demonstrated to be an efficient red-emission agent for both in vivo and in vitro bioimaging.

Highly sensitive fluorescent detection of glutathione and histidine based on the Cu(ii)-thiamine system

A novel fluorescence method for the simultaneous detection of glutathione and histidine based on their inhibitory effects on the oxidation of thiamine by Cu(ii) is proposed.