A novel "mix-response" biosensor for colorimetric and photothermal dual-mode detection of sulfide ions in food based on silver-doping Prussian blue nanoparticle

Effective identification of sulfur ions (S2-) in foodstuff is crucial for food safety and human health, but it remains challenging. Traditional single-mode colorimetric sensing methods are simple and sensitive, but are prone to interference from colored substances which can lead to false positives or negatives results. Herein, we develop a novel "mix-response" biosensor for colorimetric and photothermal dual-mode detection of S2- with good simplicity, sensitivity and portability. In this biosensor, silver-doping Prussian blue nanoparticle (SPB NPs) was used as signal output component, which not only exhibits blue color characteristics, but also has photothermal conversion properties activated by near-infrared (NIR) laser. Upon increasing the S2- concentration, the prepared SPB NPs undergo etching, leading to the formation of new silver sulfide precipitation (Ag2S), along with different colorimetric and photothermal response signals. For the portable visualization of S2-, the color information was recorded by a smartphone in combination with RGB (red channel) analysis and the evolution of the photothermal signal was documented by a thermal imager. The introduction of smartphone and handheld thermal imager in this "mix-response" biosensor makes it suitable for on-site quantitative detection of S2- without sophisticated instrument. Moreover, the development of this "mix-response" biosensor does not need the use of recognition probes (e.g. aptamers and reaction intermediates), thereby simplifying the construct procedures of sensing strategies and improving the economic efficiency of detection. More importantly, the photothermal response signals can overcome the interference of colored substances in foods, thereby reducing the false positives or negatives of the detection results.

Lysosome-targeting benzothiazole-based fluorescent probe for imaging viscosity and hypochlorite levels in living cells and zebrafish

Viscosity and hypochlorite (OCl^-) play an important role in biological activities and may cause negative effects at abnormal levels. In this study, a novel lysosome-target fluorescent probe BDHA was obtained based on a benzothiazole derivative. Probe BDHA showed linear ranges of detection for viscosity from 1.62 cP to 851.6 cP with a fluorescent turn-on response. It can also be used as a sensor for OCl^- with a turn-off response and showed a good linear range from 0 to 390 μM, with the detection limit calculated to be 2.8 μM. Moreover, BDHA can also be used to image viscosity and OCl^- levels in HeLa cells and zebrafish, owing to its excellent optical properties.

Mitochondria-Targeted Fluorescent Turn-On Probe for Rapid Detection of Bisulfite/Sulfite in Water and Food Samples

Bisulfite (HSO₃^-)/Sulfite (SO₃^2-) is widely used as a food additive, but excessive use often leads to serious consequences, so the detection of HSO₃^-/SO₃^2- is of great importance. In this paper, a novel 1,4-diethylpiperazine-modified coumarin-benzopyran derivative (probe QLP) has been synthesized and characterized. In PBS (10 mM, pH = 7.4), QLP displays good selectivity and is sensitive for HSO₃^-/SO₃^2- over various analytes with fluorescent "OFF-ON" rapid responding (2 min), long-wavelength emission (600 nm), and a detection limit of 177 nM. With the treatment of HSO₃^-/SO₃^2-, the color of the QLP solution obviously changes from blue-green to yellow, and the fluorescent color of QLP changes from colorless to amaranth. The fluorescence-enhanced mechanism is qualitatively evaluated by density functional theory calculations using the CAM-B3LYP/6-31G (d) method, which reveals that the photoinduced electron transfer leads to the fluorescence emission of the QLP-SO₃H adduct. Importantly, nontoxic QLP can be used to detect HSO₃^-/SO₃^2- in sugar, natural water samples, and living cells and localized to the mitochondria and monitor the mitochondrial HSO₃^-/SO₃^2- level.

A near-infrared emitted fluorescence probe for the detection of biosulfite in live zebrafish, mouse and real food samples

Bisulfite (HSO₃^-) has been widely used as an important food additive in daily life. Furthermore, a normal amount of HSO₃^- plays a significant role in biological systems. However, excessive intake of HSO₃^- will lead to a variety of diseases. Therefore, it is of great significance to develop an efficient fluorescent probe that can be used for detection of HSO₃^- in biological systems and food samples. In this work, a near-infrared (NIR) emitted fluorescent probe (SZY) based on hemicyanine dye was successfully synthesized and applied to detect HSO₃^- in several food samples and live animals. The proposed nucleophilic addition sensing mechanism of SZY towards HSO₃^- has been confirmed by ¹H NMR titration, high resolution mass spectrometry (HR-MS) and density functional theory (DFT) theoretical computation. The HSO₃^--induced nucleophilic reaction with α,β-unsaturated C=C binding of SZY results in the dramatic decline of the UV-vis absorption and remarkable quenching of the fluorescence emission. SZY features the advantages of near infrared emission (centered at 720 nm), high water solubility (in 98% aqueous solution), fast response time (50 s), large Stokes shift (244 nm) and low cytotoxicity. The probe SZY was successfully applied to image of HSO₃^- in live nude mouse and adult zebrafish. Semi-quantitatively analyzing the HSO₃^- level by "naked eye" in several food samples including canned fruit, white wine, white sugar and jasmine tea drinks has been realized by the colorimetric method.

Carbazole-based near-infrared-emitting fluorescence probe for the detection of bisulfite in live animals and real food samples

A carbazole-based near-infrared (NIR)-emitting fluorescent probe (QPM) was successfully developed for the detection of HSO3− in live animals and in real food samples.