Carbon nanodots as fluorescent platforms for recognition of fluoride ion via the inner filter effect of simple arylboronic acids. Experimental and theoretical investigations

Surfactant-derived water-soluble carbon dots for quantitative determination of fluoride via a turn-off–on strategy

Surfactants play a vital role as precursors for achieving carbon cores, heteroatom π-systems, and stability in carbon dots (CDs).

High quantum yield aminophenylboronic acid-functionalized N-doped carbon dots for highly selective hypochlorite ion detection

High quantum yield 3-aminophenylboronic acid-functionalized nitrogen-doped carbon dots (GAAP-CDs) were fabricated using a simple hydrothermal route and used as a sensing probe for toxic hypochlorite (ClO^-). The as-synthesized GAAP-CDs showed absorption peaks at 252, 297, and 370 nm and an emission peak at 375 nm with an excitation wavelength of 310 nm. The quantum yield of GAAP-CDs reached 58.28%, with no noticeable fluorescence change observed under high ionic strength conditions and a three-month long-term test. GAAP-CDs-based ClO^- sensing was carried out by UV-vis absorbance and fluorescence spectroscopy; the detection limit was as low as 0.77 μM (linear range of 0-100 μM), and 0.50 μM (linear range of 0.1-100 μM), respectively. In addition, the as-synthesized GAAP-CDs showed excellent selectivity towards ClO^- ions in the presence of various interfering chemicals. The satisfactory results from the proposed method of ClO^- detection in tap water and drinking water samples, suggesting promising application of GAAP-CDs for ClO^- detection.

Sensitive and selective colorimetric probe for fluoride detection based on the interaction between 3-aminophenylboronic acid and dithiobis(succinimidylpropionate) modified gold nanoparticles

APBA was conjugated on DSP@AuNP to form stable APBA–DSP@AuNP, exhibiting high selectivity towards fluoride against other anions and glucose.

Determination of Hg2+ and Cu2+ ions by dual-emissive Ag/Au nanocluster/carbon dots nanohybrids: Switching the selectivity by pH adjustment

An innovative dual-emissive ratiometric nanohybrid probe comprised of red-emitting a (Ag/Au)@insulin nanoclusters (NCs) and blue-emitting carbon dots (CDs) was designed for sensitive and selective ratiometric determination of Hg²⁺ and Cu²⁺ ions.The fluorescence intensity of CDs (λ_ex = 340 nm; λ_em = 420 nm) was unaffected in the presence of the metal ions tested, whereas the red emitting NCs (λ_ex = 340 nm; λ_em = 640 nm) was strongly quenched by both Cu²⁺ and Hg²⁺ ions. Interestingly, the selectivity of the probe toward these two ions was simply switched by controlling the pH of probe solution without using any chelating agent. The probe selectively responded to Hg²⁺ ions at acidic condition (pH = 4.0), Cu²⁺ ions at basic condition (pH = 10.0), and Hg²⁺-Cu²⁺ mixtures at pHs within this range. The respective detection limitsfor determination of Cu²⁺ and Hg²⁺ ions at their specific pH conditions were estimated as 5 nM and 7 nM, over linear ranges of 20-600 nM and 20-2000 nM, respectively. The fabricated ratiometric probe also showed distinguished fluorescence color changes to visual detection of these ions. Finally, the probe was successfully applied to determination of Hg²⁺ and Cu²⁺ ions in tap and mineral water samples.

Recent development of boronic acid-based fluorescent sensors

As Lewis acids, boronic acids can bind with 1,2- or 1,3-diols in aqueous solution reversibly and covalently to form five or six cyclic esters, thus resulting in significant fluorescence changes. Based on this phenomenon, boronic acid compounds have been well developed as sensors to recognize carbohydrates or other substances. Several reviews in this area have been reported before, however, novel boronic acid-based fluorescent sensors have emerged in large numbers in recent years. This paper reviews new boron-based sensors from the last five years that can detect carbohydrates such as glucose, ribose and sialyl Lewis A/X, and other substances including catecholamines, reactive oxygen species, and ionic compounds. And emerging electrochemically related fluorescent sensors and functionalized boronic acid as new materials including nanoparticles, smart polymer gels, and quantum dots were also involved. By summarizing and discussing these newly developed sensors, we expect new inspiration in the design of boronic acid-based fluorescent sensors.

As Lewis acids, boronic acids can bind with 1,2- or 1,3-diols in aqueous solution reversibly and covalently to form five or six cyclic esters, thus resulting in significant fluorescence changes.

Nanomaterials for the optical detection of fluoride

Overexposure to fluoride ions (F^-) causes serious diseases in human beings. Extensive efforts have been made to develop sensitive and selective approaches for F^- detection and a variety of F^- sensors have been constructed recently. The burgeoning nanotechnology has provided novel materials for F^- analysis due to the extraordinary properties of nanomaterials. In this review, we present the recent advances in different nanomaterials-based approaches for the optical F^- detection via colorimetric, fluorescent and chemiluminescent responses. The materials include gold nanomaterials, CeO₂ nanoparticles, semiconductor quantum dots, carbon quantum dots, metal-organic frameworks, upconversion nanoparticles, micellar nanoparticles, polymer dots, SiO₂ nanoparticles and graphene oxide. The recent trends and challenges in the optical detection of F^- with various nanomaterials are also discussed.