Boronate affinity-based template-immobilization surface imprinted quantum dots as fluorescent nanosensors for selective and sensitive detection of myricetin

In order to prepare a kind of efficient fluorescence sensors for determination of cis-diol-containing flavonoids, novel imprinted quantum dots for myricetin (Myr) were prepared based on boronate affinity-based template-immobilization surface imprinting. The obtained boronate affinity-based surface imprinted silica (imprinted APBA-functionalized CdTe QDs) was used as recognition elements. The quantum dots were used as signal-transduction materials. Under the optimum conditions, according to fluorescence quenching of imprinted APBA-functionalized CdTe QDs by Myr, the imprinting factor (IF) for Myr was evaluated to be 7.88. The result indicated that the boronate affinity functionalized quantum dots coated with imprinted silica were successfully prepared. The prepared imprinted APBA-functionalized CdTe QDs exhibited good sensitivity and selectivity for Myr. The fluorescence intensity was inversely proportional to the concentration of Myr in the 0.30-40 μM concentration range. And its detection limit was obtained to be 0.08 μM. Using the fluorescence sensors, the detection of Myr in real samples was successfully carried out, and the concentration of Myr in green tea and apple juice samples was evaluated to be 2.26 mg/g and 0.73 mg/g, respectively. The recoveries for the spiked green tea and apple juice samples were 95.2-105.0% and 91.5-111.0%, respectively. This study also provides an efficient fluorescent detection method for cis-diol-containing flavonoids in real samples.

Development of carbon dot-thiochrome-based sensing system for ratiometric fluorescence detection of D-penicillamine

A simple and rapid ratiometric fluorescent sensing system for D-penicillamine (D-PA) determination is developed based on yellow carbon dots (Y-CDs) combined with thiochrome (oxVB₁) for the first time. The oxidization of thiamine (VB₁) can be catalyzed by Alkaline-hydrolyzed artemisinin (a-ART) to form oxVB₁, which leads to the occurrence of fluorescence emission peak at 466 nm. Furthermore, the oxidation reaction between a-ART and VB₁ could be inhibited by D-PA, and accompanied with the decrease of fluorescence at 466 nm. However, the fluorescence peak of Y-CDs as an internal reference at 566 nm was almost unchanged. The ratiometric signal changes contributed to a robust and sensitive D-PA sensing. Under the optimal condition, a good linear response for the D-PA detection was obtained in the ranges of 0.5-50 μM with a detection limit of 0.33 μM. In addition, Y-CDs and thiochrome-based sensing system was applied to D-PA determination in real samples and obtained acceptable results. We developed a new carbon dots/thiochrome fluorescent nanoprobe for ratiometric fluorescence sensing of D-penicillamine.

A smartphone-combined ratiometric fluorescence probe for specifically and visibly detecting cephalexin

A smartphone-combined dual-emission ratiometric fluorescence probe for specifically and visibly detecting cephalexin was first designed. In the probe, blue-emitting fluorescent carbon dots (CDs) was synthesized and covered with a layer of silica spacer. Red-emitting fluorescent CdTe QDs (r-QDs) was grafted onto the silica nanospheres as an analytical probe. Then, the cephalexin antibody was covalent grafted to the ratio sensor to increase the selectivity. The ratio of fluorescence intensity (FL) of r-QDs and CDs was quenched with the increasing concentration of cephalexin. The detection method has good linear response in the range of 1-500 μM and the detection limit was 0.7 μM. Then portable device based on smartphone detection was constructed according to the color change under UV lamp. The detection image was obtained through the smartphone camera, and the color picker APP installed in the smartphone captured the RGB value of the image. In addition, this method was also used to determine the amount of cephalexin in milk samples with recovery of 94.1%-102.2%. These results showed that it was a portable, simple and visible method to detect cephalexin in food analysis and environmental monitoring.

A functional ratio fluorescence sensor platform based on the graphene/Mn-ZnS quantum dots loaded with molecularly imprinted polymer for selective and visual detection sinapic acid

A functional ratio fluorescence sensor based on the molecularly imprinted polymer (MIP) coated double quantum dots (QDs) being composited of Mn-ZnS QDs and silica-coated graphene quantum dots (GQDs@SiO₂) had been established for the sensitive, selective and visual detection of sinapic acid (SA). MIPs@Mn-ZnS/GQDs@SiO₂ was synthesized through a simple one-pot sol-gel reaction, and it exhibited two fluorescence emission peaks with yellow fluorescence of Mn-ZnS QDs at 580 nm and the blue fluorescence of GQDs at 445 nm. SA can selectively enhance the fluorescence of GQDs but quench the Mn-ZnS QDs fluorescence to the MIPs@Mn-ZnS/GQDs@SiO₂. The ratio of fluorescence enhancement to fluorescence reduction is linear with the concentration of SA from 9 to 81 nM with the detection limits of 0.8388 nM (S/N = 3). And the constructed fluorescent probe can also be used to visually detect SA according to the change of color. More importantly, molecular imprinting technique enables the sensors to selectively recognize the SA while other similar structure molecules hardly interfere with the SA determination in the measurement environment. Meanwhile, the fluorescence sensors have the advantages of fast response time and long duration of fluorescence intensity. These excellent performances made the proposed method to be applied for the determination of SA in Semen Sinapis and Descurainiae Semen.

Fluorometric detection of dopamine based on 3-aminophenylboronic acid-functionalized AgInZnS QDs and cells imaging

Herein, cysteine capped AgInZnS QDs (Cys-AIZS QDs) with a large stoke shift and excellent biocompatibility were synthesized by a one-step aqueous method, followed by modified with 3-aminophenylboronic acid (APBA). Dopamine (DA) as an important neurotransmitter in brain can lead to significantly decrease in the fluorescence intensity of 3-aminophenylboronic acid-functionalized Cys-AIZS QDs (APBA-AIZS QDs) in a large concentration range of 1.5-900 μM. Good linearity can be obtained in the range of 15-120 μM, with a limit of detection (LOD) of 0.65 μM. Moreover, Cys-AIZS QDs and APBA-AIZS QDs were applied to living cells imaging, and Cys-AIZS QDs were applied to the co-localization with lysosomes, indicative of the feasibility of intracellular detection.

Determination of cis-diol-containing flavonoids in real samples using boronate affinity quantum dots coated with imprinted silica based on controllable oriented surface imprinting approach

Novel boronate affinity imprinted quantum dots (BA-CdTe@MIPs QDs) were used to develop a selective and sensitive fluorescent nanosensor for determination of cis-diol-containing flavonoids such as quercetin (Qu), baicalein (Bai) and luteolin (Lut) based on controllable oriented surface imprinting approach. The boronate affinity imprinted silica was used as recognition elements. Under the optimum conditions, the imprinting factor (IF) for Qu, Bai and Lut was evaluated to be 9.42, 6.58 and 10.91, respectively. The results indicated that the boronate affinity quantum dots coated with imprinted silica were successfully prepared. The obtained BA-CdTe@MIPs QDs provided high selectivity and high sensitivity for cis-diol-containing flavonoids such as quercetin and luteolin. The BA-CdTe@MIPs QDs exhibited linear decrease in fluorescence intensity with the increase of concentration of quercetin in the 0.05-25 μM concentration range. The detection limit (LOD) is evaluated to be 0.02 μM. The obtained fluorescent nanosensor could be successfully applied to efficient detection of cis-diol-containing flavonoids in onion skin and human urine samples. The recoveries for the spiked onion skin and urine samples were evaluated to be 83.50-104.00% and 86.67-105.00%, respectively. Clearly, this study provides a rapid and efficient fluorescent detection tool for cis-diol-containing flavonoids in real samples.

A new fluorescent hemicryptophane for acetylcholine recognition with an unusual recognition mode

The ammonium of the target interacts with the south part of the hemicryptophane probably because the cyclotriveratrylene's electronic density is altered by the extension of conjugation.

Dual-emission ratiometric nanoprobe for visual detection of Cu(II) and intracellular fluorescence imaging

Copper is an essential mineral nutrient for the human body. However, excessive levels of copper accumulated in the body can cause some diseases. Therefore, it is great significant to establish a sensitive bioprobe to recognize copper ions (Cu²⁺) in vivo. In our work, nitrogen-doped carbon dots (N-CDs) and gold nanoclusters (Au NCs) are selected as luminescent nanomaterials and the Au NCs/N- CDs nanohybrids is successfully synthesized by coupling method. The Au NCs/N-CDs exhibited characteristic dual-emission peaks at 450 and 620 nm when excited by a single-wavelength of 380 nm. When different amounts of Cu²⁺ are introduced, the fluorescence intensity of the Au NCs is gradually weakened and fluorescence intensity of the N-CDs is almost unchanged, which can facilitate the visual detection of Cu²⁺. The Au NCs/N-CDs nanohybrid possesses good selectivity to Cu²⁺ with a limit of detection (LOD) is 3.5 μM and linear detection range of 10-150 μM. Visualization detection of Cu²⁺ is implemented by using nanoprobe in water samples. Furthermore, the ratiometric nanoprobe is utilized to the toxicity test of liver cancer cells, indicating excellent biocompatibility and low toxicity. This nanoprobe has been used to the intracellular fluorescence imaging. Moreover, this method is expected to be used to monitor the changes of Cu²⁺ concentration in hepatocytes.

Photoinduced holes transfer based visual determination of dopamine in human serum

A simple unexplored strategy was followed to construct ratiometric fluorescence-based sensing system for the detection of dopamine (DA) in human serum. Ratiometric fluorescence system was constructed through bonding energy transfer (TBET) by conjugating carboxyl functionalized CdTe quantum dots (QDs) and amine-capped Carbon quantum dots (CQDs). The photophysical properties of sensing system were characterized by standard methods. Photoluminescence (PL) of sensing system under excitonic wavelength (350 nm) depends on dual emission at 440 and 595 nm that corresponds to CQDs and CdTe QDs respectively. The developed sensing system was utilized for visual determination of DA, an unquenched blue fluorescence of CQDs in ratiometric system reveals the visual color differentiation for DA binding with CdTe QDs among the possible interferences (Alanine, Glycine, Glucose, Sucrose, Urea and Ascorbic acid). The limit of detection (LOD) and quantification (LOQ) was calculated as 8.1 and 27.2 nm respectively by using regression analysis. Photoinduced holes transfer (PHT) might have attributed the possible sensing mechanism for DA that quench the photoluminescence sequentially to enhance the sensing performance of QDs. The matrix interferences and reliability of the developed sensing platform were evaluated by testing DA spiked human serum and the sensing response was found to be field deployable.

One-step fabrication of a boric acid-functionalized lanthanide metal–organic framework as a ratiometric fluorescence sensor for the selective recognition of dopamine

A boric acid-functionalized Eu-MOF ratiometric fluorescence sensor was prepared for the selective recognition of dopamine.