Generalized ratiometric fluorescence nanosensors based on carbon dots and an advanced chemometric model

Carbon quantum dots for fluorescent detection of nitrite: A review

NO₂^- is commonly found in foods and the environment, and excessive intake of NO₂^- poses serious hazards to human health. Thus, rapid and accurate assay of NO₂^- is of considerable significance. Traditional instrumental approaches for detection of NO₂^- faced with limitations of expensive instruments and complicated operations. Current gold standards for sensing NO₂^- are Griess assay and 2,3-diaminonaphthalene assay, which suffer from slow detection kinetics and bad water solubility. The newly emerged carbon quantum dots (CQDs) exhibit integrated merits including easy fabrication, low-cost, high quantum yield, excellent photostability, tunable emission behavior, good water solubility and low toxicity, which make CQDs be widely applied to fluorescent assay of NO₂^-. In this review, synthetic strategies of CQDs are briefly presented. Advances of CQDs for fluorescent detection of NO₂^- are systematically highlighted. Lastly, the challenges and perspectives in the field are discussed.

A Cu2+-assisted fluorescence switch biosensor for detecting of coenzyme A employing nitrogen-doped carbon dots

Herein, a simple and sensitive Cu²⁺-assisted fluorescence switch biosensor for the detection of coenzyme A (CoA) was proposed by employing nitrogen-doped carbon dots (N-CDs). N-CDs were successfully synthesized by sodium alginate and melatonin via pyrolysis. The as-prepared N-CDs were spherical with an average diameter of 2.8 nm and exhibited blue emission (λ_em = 480 nm, λ_ex = 360 nm) with a high fluorescence quantum yield of 50.2%. The intense blue emission of the N-CDs could be effectively quenched by copper ions through the formation of the N-CDs/Cu²⁺ complex. With the introduction of CoA, a more stable CoA/Cu²⁺ complex formed, leading to the fluorescence recovery of N-CDs. Based on this strategy, CoA could be sensitively and selectively detected with a good linear relationship in the range of 0.02-5.00 μM and with a detection limit of 12 nM. In addition, this sensor was applied for CoA detection in human serum samples with satisfactory recovery. The results showed great potential towards advancing applications in CoA-dependent bioresearch.

Ratiometric fluorescence detection of dipicolinic acid based on Microporous Ln/melamine-terephthaladehyde schiff base networks complex

Lanthanide-based fluorescence sensor in the detection of major Anthrax biomarker dipicolinic acid (DPA) is attracting wide attention. In this work, we proposed a new strategy for ratiometric fluorescence detection of DPA based on microporous Ln/melamine-terephthaladehyde Schiff base networks (Ln/MTSNW) complex for the first time. The microporous MTSNW was prepared by amine-aldehyde condensation between melamine and terephthaladehyde and presented lamellar and octahedral structure. Lanthanide ions, Eu³⁺ or Tb³⁺ were coordinated with N atoms of MTSNW to form Ln/MTSNW complex. The microporous Ln/MTSNW complex not only provided large surface area to improve the sensitivity of DPA detection, but also constructed ratiometric fluorescence sensors to eliminate environmental effects and instrument fluctuation. DPA was a highly efficient antenna molecule for Eu³⁺ and Tb³⁺ and transferred the energy to Eu³⁺ or Tb³⁺ to sensitize their fluorescence. The Ln/MTSNW complex were uniformly and stably dispersed in aqueous solution for DPA detection with a linear range from 15 nM to 7 μM and low detection limit of 5.2 nM for Eu/MTSNW and a linear range from 4 nM to 2.5 μM and low detection limit of 1.4 nM for Tb/MTSNW. Due to the simple preparation of Ln/MTSNW complex and low technical requirement, the ratiometric fluorescence DPA sensor based on Ln/MTSNW complex might show great potential in practical applications.