One-pot synthesis of nitrogen-doped carbon dots for highly sensitive determination of cobalt ions and biological imaging

Dual-mode colorimetric and fluorescent detection of cobalt ions based on N, B co-doped carbon quantum dots and p-phenylenediamine derived nanoparticles

Nitrogen, boron co-doped carbon quantum dots (gCQDs), and a coloration probe (PPD-NPs) with response to cobalt ions (Co2+) were prepared by using 4-hydroxyphenylboric acid as the common precursor, with ethylenediamine and p-phenylenediamine (PPD) adopted as nitrogen-doped reagents, respectively. A noticeable brown-to-purple color change can be observed with the addition of Co2+, and a broad absorption band emerges at 535 nm. At the same time, gCQDs, which is introduced as the fluorescence signal source, will be significantly quenched due to the enhanced inner filtration effect, induced by the overlap between the emission spectrum of gCQDs and the emerging absorption band. Therefore, a colorimetric/fluorescent dual-mode sensing probe for Co2+ is constructed by combining the recognition unit PPD-NPs and the fluorescent gCQDs into PPD-NP/gCQD. Under the optimized experimental conditions, the calculated limits of detection are 1.51 × 10-7 M and 3.75 × 10-7 M for the colorimetric mode and the fluorescence mode, respectively, well qualified for the determination of Co2+ maximum permitted level in drinking water. The feasibility of the proposed method has been verified in tap water, lake water, and black tea samples.

Synthesis of Temperature Sensing Nitrogen-Doped Carbon Dots and Their Application in Fluorescent Ink

With the discovery of research, many properties of carbon dots are getting better and better. People have taken advantage of this and utilized them interspersed in various fields. In the present study, water-soluble nitrogen-doped carbon dots (N-CDs) with excellent optical and fluorescence thermal properties were prepared by the hydrothermal method using 4-dimethylaminopyridine and N,N'-methylenebisacrylamide as precursors. Co2+ has a selective bursting effect on the fluorescence of N-CDs. The fluorescence of N-CDs is selectively burst by Co2+, and the high sensitivity is good in the range of 0-12 μM with a detection limit of 74 nM. In addition, the good temperature response (reversible and recoverable fluorescence in the temperature range of 20~90 °C) and excellent optical properties of the N-CDs also make them new potentials in the field of fluorescent inks and temperature sensing.

Dual emission N-doped carbon dots as a ratiometric fluorescent and colorimetric dual-signal probe for indigo carmine detection

Novel dual-emission fluorescent nitrogen-doped carbon dots (N-CDs) were synthesized by a facile one-pot hydrothermal method using ascorbic acid and rhodamine B as precursors and melamine as nitrogen source. The obtained N-CDs exhibited dual-emitting peaks at 435 nm and 578 nm under the single excitation of 350 nm. The fluorescence at 578 nm was more effectively quenched by indigo carmine (IC) based on the internal filtration effect and aggregation-induced emission quenching. Meanwhile, the apparent color change of N-CDs from pink to blue-purple after adding various concentrations of IC could be clearly observed with the naked eye. Therefore, a ratiometric fluorescent and colorimetric dual-signal probe based on N-CDs was developed for IC detection with high selectivity and sensitivity. The addition of IC caused the ratiometric fluorescent value (F₄₃₅/F₅₇₈) to increase linearly within the range from 0 to100 µM with a detection limit (LOD) of 0.18 µM and the colorimetric signal presented a linear response in the range of 0-133 µM with a LOD of 57.4 nM. Furthermore, the IC in juice drink, candy, and water was successfully detected. Besides, the N-CDs were also designed as a ratiometric temperature probe, and the ratiometric fluorescence signal (F₄₃₅/F₅₇₈) was linearly and reversibly responsive to temperature in the range of 20-75 °C.

Carbon-polymer dot-based UV absorption and fluorescence performances for heavy metal ion detection

In previous reports, carbon dots (CDs) were customarily used as fluorescent probes to detect heavy metal ions. However, scientists neglected to take advantage of the excellent UV absorption properties of CDs to detect heavy metal ions. Herein, we synthesized nitrogen-containing carbon polymer dots (N-CPDs) for the determination of Co²⁺ ions in water samples by a one-step hydrothermal method using l-histidine and ethylene imine polymer as raw materials. The N-CPDs were characterized by ultraviolet-visible spectrum (UV-vis), infrared spectrum (FT-IR), X-ray photoelectron spectrum (XPS) and transmission electron microscopy (TEM) techniques. They possess superior full-band UV absorption performance and the surface is rich in multifunctional groups such as -COOH, -CN-, -OH, etc. When Co²⁺ was added to N-CPDs solution, the color of the solution rapidly changed from colorless to yellow-brown, which was visible to the naked eye. The UV absorption intensity of N-CPDs changed, and the fluorescence was instantly quenched, due to the formation of chelate between Co²⁺ and N-CPDs, and the FRET process occurred. The detection of Co²⁺ showed good linearity for both fluorescence and UV absorption spectroscopy modes in the range of 0-200 μM, and the limit of detection were 1.0023 μM and 0.75 μM, respectively. These two methods have the advantages of simple operation, remarkable selectivity and small sample size, which can be applied to the field detection of Co²⁺ in water samples. It is possible to develop the UV absorption properties of CDs to detect the ions.

Insight into the Modulation of Carbon-Dot Optical Sensing Attributes through a Reduction Pathway

Oxidized/reduced carbon dots (CDs) with tunable optical features have emerged as a new class of CDs having a common "molecular origin" but different fluorescence (FL) behaviors. In the present work, using "banana peel" as a sole carbon source followed by doping with fluorine (F), boron (B), and nitrogen (N) over CDs, banana peel-derived carbon dots (BP-CDs) were synthesized using a well-known hydrothermal synthesis method. Moreover, as-synthesized BP-CDs were further reduced to "rBP-CDs" by NaBH4. At post reduction, the FL performance (i.e., quantum yield) of rBP-CDs were found to be enhanced compared with the BP-CDs, along with variations in excitation and emission wavelengths. Interestingly, the optical sensing attributes of BP-CDs and rBP-CDs were varied, that is, BP-CDs selectively sense "Co2+ with a limit of detection (LOD) value of 180 nM", whereas rBP-CDs detected Co2+ (with an LOD value of 242 nM) as well as Hg2+ (with an LOD value of 190 nM). To the best of our knowledge, this work presents the very first report on the modulation of CDs' sensing behavior after reduction. The modulation in the sensing behavior with the common carbon precursor and reduction paves a new possibility for exploring CDs for different commercial applications.

Nitrogen and boron co-doped carbon dots as a novel fluorescent probe for fluorogenic sensing of Ce4+ and ratiometric detection of Al3

Carbon dots have been widely focused on the field of metal ion detection due to their excellent optical property. Herein, novel orange fluorescent nitrogen and boron co-doped carbon dots (NB-CDs) are obtained by one-pot solvothermal using p-phenylenediamine and boric acid as raw materials. The NB-CDs exhibit excitation-independent emissions and the maximum emission wavelength is 597 nm at 420 nm excitation. The fluorescence can be quenched by Ce⁴⁺ effectively and selectively, and the detection range of Ce⁴⁺ is gained from 0.14 to 180 μM with a detection limit of as low as 0.14 μM. Furthermore, Al³⁺ can also recombine with NB-CDs surface functional groups, which shows a detection range from 1.07 to 100 μM and a detection limit of as low as 1.07 μM, accompanied with a blue-shift to 527 nm.

Green-emission nitrogen-doped carbon quantum dots from alkaline N-methyl-2-pyrrolidinone for determination of β-galactosidase and its inhibitors

A new fluorescence method was established for sensitive detection of β-galactosidase (β-gal) activity in spiked human serum and screening of inhibitor. Nitrogen-doped carbon quantum dots (N-CQDs) were prepared by solvothermal polymerization of N-methyl-2-pyrrolidinone in an alkaline condition. The colloidal N-CQDs exhibit good water solubility, stability, and emit bright green fluorescence with a maximum emission peak at 528 nm upon excitation at 420 nm. β-gal specifically catalyzes the decomposition of its substrate P-nitrophenyl-β-D-galactopyranoside into 4-nitrophenol, whose absorption spectrum overlaps well with the excitation spectrum of the N-CQDs. As a result, the fluorescence of the N-CQDs is remarkably quenched by 4-nitrophenol via an inner filter effect. The sensing platform presents a linear response range for β-gal activity from 0.05 to 3.0 U·L^-1 with a low limit of detection of 0.023 U·L^-1. An acceptable precision is obtained with a relative standard deviation (RSD) of 3.1% for 1.0 U·L^-1 β-gal (n = 11). The method was applied to determine β-gal in spiked human serums with recoveries in the range  96.3-104.7%. The method was employed to evaluate inhibitor screening with D-galactal and chloroquine diphosphate as models.

A label-free fluorescence nanosensor based on nitrogen and phosphorus co-doped carbon quantum dots for ultra-sensitive detection of new coccine in food samples

In this paper, an innovative method for the sensitive detection of new coccine using N, P-doped carbon quantum dots (N,P-CQDs) as fluorescent nanosensor is reported for the first time. The sensing mechanism is based on the fluorescence quenching of N,P-CQDs by new coccine through inner filter effect (IFE). N,P-CQDs were prepared by simple hydrothermal treatment of citric acid, phosphoric acid and ethylenediamine. Under the optimal conditions, the new coccine has two good linear responses in the concentration range of 0.2-100 and 100-200 μM, and the detection limits are as low as 24.8 and 9.4 nM, respectively. Our developed nanosensor has been successfully used for the determination of new coccine in food samples with good precision and high accuracy. This work highlights the economic, rapid, simple, selective and ultra-sensitive for new coccine detection, and opens up a new way for the monitoring of new coccine in actual food samples.

Utilization of waste biomass of Poa pratensis for green synthesis of n-doped carbon dots and its application in detection of Mn2+ and Fe3

In this study, a novel and sustainable approach was used to synthesize nitrogen-doped carbon dots (NCDs) from the waste biomass of Poa Pratensis (Kentucky bluegrass (KB)) by a facile hydrothermal method. The prepared KBNCDs were subjected to various characterization techniques, including X-ray diffraction, X-ray photoelectron spectroscopy, transmission electron microscopy, and Fourier-transform infrared spectroscopy to verify the formation of carbon dots and their surface functional groups. The KBNCDs exhibited good hydrophilic fluorescence (FLU) properties with an acceptable quantum yield (7%). The synthesized KBNCDs showed excitation wavelength-dependent FLU emission behavior with strong cyan-blue FLU upon irradiation with 365 nm UV-light. The hydrophilic optical properties of the as-synthesized KBNCDs were used to detect Fe³⁺ and Mn²⁺ ions in an aqueous medium with good selectivity and sensitivity. It was found that the FLU of the KBNCDs is quenched in the presence of Fe³⁺ and Mn²⁺ ions, and the quenching rate was linear with the concentration of Fe³⁺ and Mn²⁺ ions. The limit of detection (LOD) of KBNCDs with metal ions was calculated using the Stern-Volmer relationship. The LOD values for Fe³⁺ or Mn²⁺ ions were calculated as 1.4 and 1.2 μM, respectively with the detection range from 5.0 to 25 μM. Based on these results, this study provides an underpinning for the development of KBNCD as FLU sensors that can be used in aqueous media.