Construction of CDs@ß-CD@CCM ratiometric fluorescence probe for FRET-based ClO--sensing.

ß-Cyclodextrin (ß-CD)-functionalized carbon quantum dots (CDs) loaded with curcumin (CCM) were used for ClO-sensing with high sensitivity and selectivity. This fluorescence resonance energy transfer (FRET)-based sensor was created through attaching CCM to the CDs via ß-CD linker. CCM could get into the interior of ß-CD triggering the FRET from CDs to CCM, providing an 'off' state of the CDs. However, the effect of FRET was weakened by the ClO-, because the o-methoxyphenol structure from CCM was oxidized to be benzoquinone. The fluorescence intensity of CDs@ß-CD@CCM at 440 nm can be heightened and 520 nm from CCM can decrease along with the increased ClO-. Therefore, a ratiometric fluorescence probe for ClO-sensing is successfully constructed. It conforms to a polynomial curve equation which is I440/I520= -0.0268 + 0.0315 CClO-+ 0.0055[CClO-]2(R2= 0.9958) between 0 and 18.4µM ClO-. Furthermore, we also obtain excellent results using this spectrophotometric method for ClO--sensing in pure water and commercial disinfectants, which afford potential in the environment monitoring area. We expect this sensing platform could be helpful in other analogous probes in relevant fields.

Construction of CdTe@γ-CD@RBD nanoprobe for Fe3+-sensing based on FRET mechanism in human serum.

A Fe3+ optical sensor (CdTe@γ-CD@RBD) has been developed by using gamma-cyclodextrin (γ-CD) as a bridge to link CdTe quantum dots (QDs) and a Rhodamine B derivative (RBD). The RBD molecule can enter the cavity of the γ-CD anchored onto the surfaces of the QDs. In the presence of Fe3+, the fluorescence resonance energy transfer (FRET) process from QDs to RBD will be initiated, rendering the nanoprobe to display a response to Fe3+. The degree of fluorescence quenching presented a satisfactory linearity between 10 and 60 µΜ with the incremental concentrations of Fe3+, and the calculated limit of detection was 2.51 µΜ. Through sample pretreatment procedures, the probe has been used in the determination of Fe3+ in human serum. The average recoveries in the spiking levels are ranged from 98.60 % to 107.20 % with a relative standard deviation of around 1.43 %-2.96 %. This finding leads to a method for fluorescent detection of Fe3+ with high sensitivity and exceptional selectivity. We believe that this study can give a new insight into the rational design and application of FRET-based nanoprobes.

Self-assembled nanoplatforms with ZIF-8 as a framework for FRET-based glutathione sensing in biological samples.

A glutathione (GSH) optical sensor with high sensitivity and exceptional selectivity was established for the first time. Zeolitic imidazolate framework-8 (ZIF-8) as a model was used for the first time to entrap Mn2+:ZnS quantum dots (QDs) and a rhodamine B derivative (RBD) by self-assembly. Benefiting from the confinement effect of ZIF-8, the loaded QDs and RBD can be brought into close proximity for energy transfer to occur. In the presence of GSH, the fluorescence resonance energy transfer (FRET) process from the QDs to RBD can be initiated, rendering the fluorescent nanoprobe to exhibit a response to GSH. The fluorescence intensity of Mn2+:ZnS@ZIF-8@RBD decreased with an increase in the GSH concentration in the linear range of 5-120 µM and a detection limit of 1.5 µM. This finding leads to a method for the fluorescence detection of GSH with excellent selectivity over other reactive thiols. Moreover, because of its good accuracy and excellent recovery, the nanoplatform can be applied for GSH sensing in real human serum and urine samples. Hence, the developing probe may be extended to other optical sensing domains or drug carriers and has tremendous potential in the field of biomedicine.