Ce4+/Ce3+ as the switch of AIE-copper nanoclusters for highly selective detection of ascorbic acid in soft drinks

An ultrasimple "turn-on" sensor for indirectly detecting ascorbic acid (AA) was prepared using N-acetyl-L-cysteine stabilized copper nanoclusters (NAC-CuNCs) via the AIE (aggregation-induced emission) effect controlled by Ce4+/Ce3+ redox reaction. This sensor fully utilizes the different properties of Ce4+ and Ce3+. Non-emissive NAC-CuNCs were synthesized by a facile reduction method. NAC-CuNCs easily aggregate in the presence of Ce3+ due to AIE, resulting in fluorescence enhancement. However, this phenomenon cannot be observed in the presence of Ce4+. Ce4+ possesses strong oxidizing ability and produces Ce3+ by reacting with AA via a redox reaction, followed by switching on the luminescence of NAC-CuNCs. Moreover, the fluorescence intensity (FI) of NAC-CuNCs increases with the concentration of AA in the range of 4-60 µM, with the limit of detection (LOD) as low as 0.26 µM. This probe with excellent sensitivity and selectivity was successfully used in the determination of AA in soft drinks.

Paracetamol-Mediated Synthesis of Silver Nanoparticles and Their Functionalization with Ionic Liquid for the Colorimetric Biosensing of Ascorbic Acid

Ascorbic acid is a vital biomolecule for human beings. When the body's level of ascorbic acid is abnormal, it can lead to a number of illnesses. Its appropriate concentration is necessary for the oxidation of prostaglandins and cyclic adenosine monophosphate, the production of dopamine, norepinephrine, epinephrine, and carnitine, and the expansion and durability of the collagen triple helix in humans. In the present work, silver nanoparticle synthesis was performed through a paracetamol-mediated approach. Different characterization techniques, such as X-ray diffractometry (XRD), energy dispersive X-ray (EDX), Fourier transform infrared (FTIR), and scanning electron microscopy (SEM), were used to confirm the prepared nanoparticles. Subsequently, the prepared Ag NPs functionalized with an ionic liquid were used as a sensing platform for ascorbic acid in blood serum samples. To achieve the best possible results, the proposed biosensor was optimized with different parameters such as TMB concentration, time, amount of capped nanoparticles (NPs), and pH. The proposed biosensor offers a sensitive and straightforward method for ascorbic acid with a linear range from 2 × 10-9 to 3.22 × 10-7 M, an LOD of 1.3 × 10-8 M, an LOQ of 4.3 × 10-8 M, and an R2 of 0.9996, Moreover, applications of the proposed biosensor were successfully used for the detection of ascorbic acid in samples of human plasma, suggesting that Ag NPs with high peroxidase-like activity, high stability, and facile synthesis exhibited promising applications in biomedical fields.

An electrostatic repulsion strategy for a highly selective and sensitive “switch-on” fluorescence sensor of ascorbic acid based on the cysteamine-coated CdTe quantum dots and cerium(iv)

A highly selective “switch-on” fluorescence approach for sensing of ascorbic acid (AA) based on the system of CA-CdTe QDs-Ce⁴⁺-AA was developed.

Fluorescence Turn-On Detection of Ascorbic Acid Using a Self-Assembled Lanthanide Polymer Nanoparticle

Ascorbic acid (AA), or vitamin C, is an important reactive biological molecule in vivo, and an abnormal level of AA is associated with many diseases. Therefore, the rapid, sensitive, and selective detection of AA levels is of significance in cases of medical assay and diagnosis. Compared with other nanoparticles, lanthanide coordination polymer nanoparticles (Ln-CPs) have been demonstrated as the excellent biomolecule sensing platforms due to their unique optical properties and intrinsic porosities. In this work, the cerium coordination polymer nanoparticles ATP-Ce-Tris were synthesized in a simple and quick way. The synthesized ATP-Ce-Tris nanoparticle shows the characteristic peak of Ce³⁺ located at 365 nm, which is corresponding to the 4f→5d transition of Ce³⁺. In the presence of Fe³⁺, the fluorescence of ATP-Ce-Tris quenched, and the following added ascorbic acid (AA) makes it restoring effectively. Based on this, we constructed a fluorescence probe with excellent sensitivity for AA sensing in a wide linear relationship from 0.05 to 500 μM. The detection limit was as low as 18 nM (signal-to-noise ratio of three), which is one or two orders of magnitude lower than those of reported sensors. The proposed sensing systems also exhibits excellent sensitivity for AA detection in human serum sample, exploiting a valuable platform for AA analysis in clinic diagnostic and drug screening.

Water-dispersed silicon quantum dots for on-off-on fluorometric determination of chromium(VI) and ascorbic acid

Water-dispersed silicon quantum dots (SiQDs) with the quantum yield of 25% was prepared using aminopropyltrimethoxysilane as the silicon source and ascorbic acid (AA) as the reduction reagent. The SiQDs display blue fluorescence with excitation/emission peaks at 350 nm/440 nm. The synthesized SiQDs are shown to be a viable "on-off-on" fluorescent probe for the detection of Cr(VI) and AA. Cr(VI) ions exert an inner filter effect on the fluorescence of the SiQDs which results in a reduction of fluorescence (off-state). On addition of AA, Cr(VI) is chemically reduced to Cr(III) which weakens the inner filter effect and restores fluorescence (on-state). The method has low detection limits for both Cr(VI) and AA (0.16 μM and 0.57 μM, respectively). It was applied to the analysis of spiked lotus seeds and human serum samples. Graphical abstract A simple and facile "on-off-on" fluorometric method for Cr(VI) and ascorbic acid (AA) was developed using water-soluble silicon quantum dots (SiQDs) as the fluorescent probe. The approach was also used to assay Cr(VI) and AA in the lotus seeds and human serum, respectively.

New strategy for the azido–ascorbic acid reaction: a convenient chemosensor and its imaging in garlic slice tissues

Three chemosensors with azide groups at different sites were designed for rapid detection of ascorbic acid in garlic slice tissues.

A rapid microwave synthesis of nitrogen-sulfur co-doped carbon nanodots as highly sensitive and selective fluorescence probes for ascorbic acid

A ultrafast one-step microwave-assisted method was developed for the synthesis of nitrogen-sulfur co-doped carbon nanodots (N,S-CDs) by using ethylenediamine as the carbon source and sulfamic acid as the surface passivation reagent. The morphology and the properties of N,S-CDs were explored by a series of techniques, such as high-resolution transmission electron microscopy, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, UV-vis absorption and fluorescence spectroscopy. The prepared N,S-CDs exhibit bright blue photoluminescence with a high fluorescence quantum yield (FLQY) up to 28%, and high stability and excellent water solubility. A N,S-CDs-based fluorescent probe was developed for sensitive detection ascorbic acid (AA) in the presence of Cu(2+), based on the mechanism that AA reduces Cu(2+) to Cu(+), then Cu(+) quenches the fluorescence of N,S-CDs through electron or energy transfer due to the interaction between Cu(+) and thiol ligand on the N,S-CDs surface. The observed linear response concentration range was from 0.057 to 4.0μM to AA with a detection limit as low as 18nM. The probe exhibited a highly selective response toward AA even in the presence of possible interfering substances, such as uric acid and citric acid. Moreover, these promising features made the sensing system used for the analysis of human serum and urine samples.

Application of graphene quantum dots decorated with TEMPO-derivatized zinc phthalocyanine as novel nanoprobes: probing the sensitive detection of ascorbic acid

A nanocomposite of (2,2,6,6-tetramethylpiperidin-1-yl)oxyl substituted zinc phthalocyanine and graphene quantum dots is a selective fluorescence sensor for ascorbic acid.

Graphene quantum dots as selective fluorescence sensor for the detection of ascorbic acid and acid phosphatase via Cr(vi)/Cr(iii)-modulated redox reaction

A facile and rapid fluorescence assay based on a redox reaction for successively detecting ascorbic acid and acid phosphatase was developedviaCr(vi)-modulated graphene quantum dots (GQDs).

Long-wavelength analyte-sensitive luminescent probes and optical (bio)sensors

Long-wavelength luminescent probes and sensors become increasingly popular. They offer the advantage of lower levels of autofluorescence in most biological probes. Due to high penetration depth and low scattering of red and NIR light such probes potentially enable in vivo measurements in tissues and some of them have already reached a high level of reliability required for such applications. This review focuses on the recent progress in development and application of long-wavelength analyte-sensitive probes which can operate both reversibly and irreversibly. Photophysical properties, sensing mechanisms, advantages and limitations of individual probes are discussed.