Quantum dots modified with the Al(III)-pefloxacin complex as a novel bioprobe for the sensitive turn-on and dual-fluorescence detection of dsDNA

Dual-band fluorescence detection of double-stranded DNA with QDs-Mn2+-pefloxacin

By integrating the fluorescence of quantum dots (QDs) and Mn²⁺-pefloxacin mesylate (Mn²⁺-pefloxacin), a new type of dual-band fluorescence biosensor for high-efficiency and sensitive determination of double-stranded DNA (dsDNA) is developed. The biosensor is based on the fluorescence "OFF-ON" mode of both QDs and QDs-Mn²⁺-pefloxacin. The Mn²⁺-pefloxacin complex can quench the QDs fluorescence via photoinduced electron transfer (PET), and its fluorescence is also quenched. Due to the specificity and strong binding affinity of dsDNA for the Mn²⁺-pefloxacin complex, it can break the low fluorescent QDs-Mn²⁺-pefloxacin and restore the fluorescence of QDs and Mn²⁺-pefloxacin complex in their respective bands. Therefore, the dual-band fluorescence quantitative detection of dsDNA by QDs-Mn²⁺-pefloxacin can be achieved, while bovine serum albumin, single-stranded DNA, and bio-related ions do not yield similar results. Furthermore, the possible reaction mechanisms are systematically discussed. The detection limits (3δ/K) of herring sperm (hs) DNA in the fluorescence recovery bands of QDs and Mn²⁺-pefloxacin complex are 0.0142 and 0.0465 μg/mL, respectively. The developed biosensor was used for dsDNA detection in synthetic samples, and desirable results are obtained.

Profiling the interaction of Al(III)-GFLX complex, a potential pollution risk, with bovine serum albumin

Fluoroquinolone antibiotics (FQs), a new class of pollutants that seriously threaten human health through environmental and food residues, have aroused wide public concern. However, little attention has been paid to the potential toxicity of FQs' metal complex. Here, we firstly explore the proof-of-concept study of FQs' metal complex to bind bovine serum albumin (BSA) using systematical spectroscopic approaches. In detail, we have found that the complex of Al³⁺ with gatifloxacin (Al(III)-GFLX complex) can effectively bind to BSA via electrostatic interaction in PBS buffer (pH = 7.4, 1×), resulting in the formation of Al(III)-GFLX-BSA complex. The negative value of ΔG shows that the binding of Al(III)-GFLX complex to BSA is a spontaneous process. Circular dichroism spectra verify that Al(III)-GFLX complex effectively triggers the conformation changes of BSA's secondary structure. It has been proved that the interaction of small molecule with serum albumin has a significant effect on their in vivo biological effects such as absorption, distribution, metabolism, and excretion, and etc. Therefore, the results of this paper may offer a valuable theoretical basis for establishing safety standards of FQs' metal complex to ensure food and environmental health.

Activatable QD-Based Near-Infrared Fluorescence Probe for Sensitive Detection and Imaging of DNA

Accurate detection of DNA is essential for the precise diagnosis of diseases. Here we report an activatable near-infrared (NIR) fluorescence nanoprobe (QD-Al-GFLX) composed of NIR quantum dots (QDs) and Al(III)-gatifloxacin (Al-GFLX) complexes for the sensitive detection of double-stranded DNA (dsDNA) both in aqueous solution and in living cells. We demonstrated that the initial strong NIR fluorescence of QDs in QD-Al-GFLX was quenched by the Al-GFLX complex via a photoinduced electron transfer (PET) mechanism. Upon interaction with dsDNA, the high binding affinity between dsDNA and Al-GFLX complex could trigger QD-Al-GFLX dissociation, which could eliminate the PET process, resulting in significant enhancement of NIR fluorescence. QD-Al-GFLX was sensitive and specific to detect dsDNA in aqueous solution, with a detection limit of 6.83 ng/mL. The subsequent fluorescence imaging revealed that QD-Al-GFLX holds a high ability to enter into live cells, generating strong NIR fluorescence capable of reporting on dsDNA levels. This study highlighted the potential of using QD-Al-GFLX nanoprobe for the real-time detection and imaging of dsDNA in living cells.