Multi-mode fluorescence sensing detection based on one core-shell structure quantum dots via different types of mechanisms

Polyvinyl alcohol-derived-carbon quantum dots based fluorometric "On-Off" probe for moxifloxacin detection in milk and egg samples

Unconditional use of antibiotics triggered the process of bacterial resistance and causes major health problems. Nowadays, antibiotics majorly used in animals not only for infection treatment but also as mass promotor. The excess amount of antibiotics residue in animal derived foods which accelerate antibiotic resistance (ABR). So, here, a simple and quick carbon quantum dots(CQDs) based fluorometric "On-Off" probe was developed for detection of moxifloxacin (MOXI) in milk and egg samples. The CQDs emits blue emission and are uniformly distributed with average particle size 5.9 ± 0.22 nm. With MOXI, fluorescence intensity of CQDs at 372 nm decreased due to inner filter effect (IFE) and a new peak appeared at 508 nm correspondence to MOXI. The probe shows linear response with MOXI concentration varies as 0.025 µM - 15.0 µM with lower detection limit (LOD) of 6.34 nM. The real sample applicability test proved that the sensors have excellent efficacy for food applications.

Transient absorption study on fluorescence quenching of InP/ZnS quantum dots by MXene

Fluorescence quenching due to energy transfer from InP/ZnS quantum dots (QDs) to Ti3C2Tx MXene materials was investigated by the transient absorption spectroscopy. During the fluorescence quenching, the photo-induced absorption feature in the transient spectrum was blue-shifted due to the higher photon energy required for the upward transition. The lifetime of stimulated emission was gradually extended from 0.86 μs to 2.28 μs with increasing Ti3C2Tx MXene. The fluorescence quenching of QDs can be quantitatively characterized by analyzing the lifetime of the stimulated emission feature in the transient absorption spectrum, which was used as a Ti3C2Tx MXene detection with the sensitivity of 6.63 mL/mg. The results of this study provide the basis for the design of optical sensors.

Analyte-triggered cascade signal amplification strategy for highly sensitive detection of iodate in table salt with dual-readout signals

A novel and highly sensitive upconversion fluorescence and colorimetric dual readout iodate (IO₃^-) nanosensor system was constructed by using both the outstanding optical performance of NaYF₄:Yb, Tm upconversion nanoparticles (UCNPs) and the analyte-triggered cascade signal amplification (CSA) technique. The construction of the sensing system consisted of three processes. First, IO₃^- oxidized o-phenylenediamine (OPD) to diaminophenazine (OPDox), while IO₃^- was reduced to I₂. Second, the generated I₂ can further oxidize OPD to OPDox. This mechanism has been verified by ¹H NMR spectra titration analysis and HRMS measurement, which effectively improves the selectivity and sensitivity of the measurement of IO₃^-. Third, the generated OPDox can effectively quench the fluorescence of UCNPs via the inner filter effect (IFE), realize analyte-triggered CSA, and allow quantitative determination of IO₃^-. Under the optimized conditions, the fluorescence quenching efficiency showed a good linear relationship to IO₃^- concentration in the range of 0.06-100 μM, and the detection limit reached 0.026 μM (3RSD/slope). Moreover, this method was applied to detect IO₃^- in table salt samples, yielding satisfactory determination results with excellent recoveries (95.5-105%) and high precision (RSD <5.5%). These results suggest that the dual-readout sensing strategy with well-defined response mechanisms has promising application prospects in physiological and pathological studies.

Surface state dominated and carbon core coordinated red-emitting carbon dots for the detection of Cr2O72- and cell imaging

Cr(VI) as a toxic heavy metal ion can easily enter into the body through drinking or eating and cause liver and kidney diseases as well as cancer. Considering its high biological toxicity and adverse effects on human body, it is desirable to develop a probe to monitor its level in the environment. Herein, a high-efficiency fluorescent nanoprobe based on red emissive carbon dots (R-CDs) was established through a convenient solvothermal strategy. The as-prepared CDs with excitation-independency had the fixed emission wavelength at 627 nm when the excitation wavelength was 560 nm. Further study manifested that the new surface state formed by nitrogen and sulfur doping and the increased conjugated system established through dehydration and carbonization were the main reasons for the fluorescence redshift. In this system, these R-CDs as a fluorescent probe exhibited high specificity and sensitivity to Cr₂O₇^2- with the linear range of 4-40 μΜ and the limit of detection could reach 80.00 nM. The quenching of these CDs by Cr₂O₇^2- was efficiently induced through a static quenching process. Meanwhile, the obtained CDs could enter into HeLa cells through endocytosis and exhibit bright red fluorescence in cells under a confocal laser scanning microscope. Thus, this work provided a promising probe not only for detecting Cr(VI) in natural environment but also for imaging in cells.

Mitochondria-targeted acridine-based dual-channel fluorescence chemosensor for detection of Sn4+ and Cr2O72- ions in water and its application in discriminative detection of cancer cells

The goal of the present work was to fabricate a new low-cost, easy-to-prepare, dual-channel fluorescence chemosensor comprised of acridine-diphenylacetyl moieties (NDA) to enable remarkable Sn⁴⁺ detection in water and biological medium. The resulting NDA-Sn⁴⁺ complex was utilized for the distinguished identification of Cr₂O₇^2- ions from other anions and biomolecules. These investigations involve the absorption, fluorescence, and electrochemical methods for the detection of Sn⁴⁺ and Cr₂O₇^2- ions in pure water. The mechanism for NDA-mediated Sn⁴⁺ detection was experimentally determined by FT-IR, NMR titrations, mass (ESI) analyses, and DFT calculations. The obtained results indicate that the NDA chemosensor possessed excellent performance characteristics including good water solubility and compatibility, quick response time (less than 10 s), high sensitivity (Sn⁴⁺ = 0.268 μM and Cr₂O₇^2- = 0.160 μM), and selectivity against coexisting metals, anions, amino acids, and peptides. The chemosensor NDA induced negligible toxicity in live cells and was successfully utilized as a biomarker for the tracking of Sn⁴⁺ in human normal and cancer cells. More importantly, NDA demonstrates distinguished recognition of Sn⁴⁺ in human cancer cells rather than in normal live cells. Additionally, NDA was shown to act as a mitochondria-targeted probe in FaDu cells.

Fluorescence-Based Sensing of Pesticides Using Supramolecular Chemistry

The detection of pesticides in real-world environments is a high priority for a broad range of applications, including in areas of public health, environmental remediation, and agricultural sustainability. While many methods for pesticide detection currently exist, the use of supramolecular fluorescence-based methods has significant practical advantages. Herein, we will review the use of fluorescence-based pesticide detection methods, with a particular focus on supramolecular chemistry-based methods. Illustrative examples that show how such methods have achieved success in real-world environments are also included, as are areas highlighted for future research and development.