Highly sensitive fluorescent probes for selective detection of hypochlorite: Applications in blood serum and cell imaging

Being one of the vital reactive oxygen species (ROS), abnormal level of hypochlorite ion (ClO^-) may pose detrimental threats to living organisms. Therefore, highly selective, and rapid monitoring of ClO^- in living system is of prime importance to protect living organisms from its harmful effects. In this regard, design of synthetic fluorescent probes for ClO^- has garnered considerable attention. However less fluorescence emission in aggregated state and less photostability of several existing probes for ClO^- inspired us to design aggregation induced emission (AIE) active fluorescent probes SH1 and SH2. Probes were rationally designed by introducing thiourea moiety that selectively reacted through desulfurization reaction and resulted in highly selective detection of ClO^-. Hypochlorite induced desulfurization reaction was validated through ¹H NMR titration and DFT studies. Fine tuning of probes SH1 and SH2 prompted highly sensitive nanoscale (55 nM and 77 nM) and rapid (15 and 35 sec) detection of ClO^-. Probe SH1 displayed less cytotoxic effect to live cells before it was successfully applied for bioimaging of ClO^- in live MCF-7 cells. Moreover, probes displayed excellent sensing potential for ClO^- in blood serum and real water samples. Advantageously, probe coated portable fluorescent films were fabricated for the easy and fast monitoring of ClO^-. Of note, this work offers excellent design strategy for highly selective detection of ClO^- that may lead to clinical trials.

Ratiometric and colorimetric probes with large stokes shift for sensing of exogenous hypochlorite in potato sprouts and industrial effluents

Being one of the important reactive oxygen species (ROS), hypochlorite ions (ClO^-) are involved in the control of several pathological and physiological processes. However, overexpression of ClO^- may prompt several disorders including cancer. Therefore, two fluorescein functionalized compounds with catechol (probe 1) and 2-naphthyl (probe 2) as substituents were synthesized through Schiff base reaction to recognize ClO^- in food items and industrial samples. While probe 2 exhibited turn-off fluorescent response towards ClO^- with limit of detection (LOD) of 86.7 nM, structurally alike probe 1 showed excellent ratiometric response with low detection limit (36.3 nM), large Stokes shift (353 nm), and 'fast' response time (15 s). ¹H NMR titration experiments favored spiroring opening of probe 1 upon the reaction with ClO^-. Probe 1 was successfully utilized for the monitoring of exogenous ClO^- in industrial samples. Further, fabrication of probe coated fluorescent paper strips and recognition of ClO^- in sprouting potato show diverse practical applicability of our probes.

Development of AIEE active fluorescent and colorimetric probe for the solid, solution, and vapor phase detection of cyanide: smartphone and food applications

Apart from environmental implications, the extreme toxicity of cyanide can lead to sudden human death upon prolonged exposure to it. Hence, rapid and low-level on-site detection of cyanide has earned paramount significance in the present era. Therefore, an AIEE active and piezofluorochromic Schiff base (probe 2) was synthesized which exhibited highly selective fluorescence enhancement based nanoscale (LOD; 6.17 nM) detection of CN^-. The interaction mode was attributed to the deprotonation of the probe by the cyanide that was confirmed through ¹H NMR titration, pH, theoretical studies, and switchable fluorescence response upon the addition of HCl. Advantageously, probe 2 displayed solid and vapor phase recognition of cyanide which is the first of its kind as far as we know. The excellent sensing potential of the probe was satisfactorily applied for the detection of cyanide in food, natural soil, and industrial wastewater. Additionally, probe 2 showed an immediate colorimetric response towards cyanide which was favorably integrated through a smartphone. Finally, the switchable fluorescence response of the probe was used to design an INHIBIT logic gate. Therefore, the multifunctional probe 2 displayed excellent practical potential for cyanide detection which was the ultimate goal of our work.

Aggregation induced emission based fluorenes as dual-channel fluorescent probes for rapid detection of cyanide: applications of smartphones and logic gates

Rational modification of molecular structure by incorporating electron donating groups can play a potential role for designing aggregation induced emission (AIE) active fluorescent probes. Based on this principle, fluorescent probes (1a–c) were synthesized, and they displayed excellent aggregation induced emission (AIE) behavior in a H₂O/DMF (4 : 1, v/v) mixture due to restrictions in intramolecular charge transfer (ICT). As a comparison, probe 1d was synthesized by installing an electron withdrawing (–NO₂) group that surprisingly quenched the aggregation behaviour. Additionally, AIE active probes 1a–c displayed a highly sensitive dual channel (fluorometric and colorimetric) response towards rapid detection of CN⁻, which is an active toxic material. Probes 1a–c showed selectively enhanced fluorescence emission behavior towards CN⁻ with detection limits of 1.34 ppb, 1.38 ppb, and 1.54 ppb, respectively. The sensing mechanism involves Michael type adduct formation due to the nucleophilic addition reaction of cyanide with probes and was confirmed through ¹H NMR titration experiments. In contrast, probe 1d containing an electron withdrawing moiety showed insensitivity towards CN⁻. Therefore, this study provides the efficient strategy to induce AIE character in fluorescent probes and expands the mechanistic approach toward the sensing of toxic CN⁻.

Rational modification of molecular structure by incorporating electron donating groups can play a potential role for designing aggregation induced emission (AIE) active fluorescent probes.

Aggregation-Induced Emission of Quinoline Based Fluorescent and Colorimetric Sensors for Rapid Detection of Fe3+ and 4-Nitrophenol in Aqueous Medium

New quinoline based fluorescent sensors 4 and 5 were rationally synthesized that exhibited excellent aggregation induced emission (AIE) in an aqueous medium. High fluorescence emission of sensors was accompanied by a noticeable redshift in their absorption and emission spectra that corresponds to the formation of J-aggregates. An AIE feature of sensors 4 and 5 was used for selective detection of Fe³⁺ and 4-NP in an aqueous medium that is attributed to the involvement of intermolecular charge transfer (ICT). The interaction mechanism of sensors with Fe³⁺ and 4-NP was investigated through ¹H NMR titration, Jobs plots, dynamic light scattering (DLS), and DFT analysis. The fluorescence quenching response of sensors 4 and 5 displayed distinguished linear behavior with the concentrations of Fe³⁺ and limits of detection (LOD) were calculated to be 15 and 10 nM, respectively. Further, LOD of sensors 4 and 5 for 4-NP (7.3 and 4.1 nM, respectively) was very low compared to previously reported sensors. Moreover, sensors' coated test strips were fabricated for solid-supported detection of Fe³⁺ and 4-NP. Sensors were successfully applied for the detection and quantification of Fe³⁺ and 4-NP in real water samples. Additionally, sensors were used for the determination of trace amounts of Fe³⁺ in the human serum sample.

Fluorescein based fluorescent and colorimetric sensors for sensitive detection of TNP explosive in aqueous medium: Application of logic gate

Rapid detection of 2,4,6-trinitrophenol (TNP) in real samples has recently attained considerable attention from the perspective of national security, human health, and environmental safety. In this context, cost-effective and convenient detection of TNP explosive was accomplished through two new fluorescein based sensors F2 and F3. Sensors displayed effective fluorescence quenching response towards TNP in the aqueous medium. Highly sensitive fluorescence detection of TNP explosive (detection limit, 0.73 (F2) and 1.7 nM (F3)) was governed by ground-state charge transfer complex formation, facilitated by favorable H-bonding between sensor and TNP explosive. Fluorescence quenching mechanism for the detection of TNP explosive was investigated through UV-Visible absorption, dynamic light scattering (DLS), density functional theory (DFT) calculations, the Benesi-Hildebrand, and Job's plots. Advantageously, sensors displayed selective and immediate colorimetric recognition of TNP explosive. Importantly, sensors exhibited quick response time towards TNP even in the presence of potential interferences that make them highly suitable for practical applications. Sensors were successfully applied for fluorescent and colorimetric detection of TNP explosive in industrial water samples and fabrication of logic gates. Further, convenient contact mode and instant surface sensing of TNP explosive were achieved through the fabrication of fluorescent strips and explosive responsive test kits.

Fluorenone-Based Fluorescent and Colorimetric Sensors for Selective Detection of I- Ions: Applications in HeLa Cell Imaging and Logic Gate

Fluorenone-based fluorescent and colorimetric sensors 1 and 2 have been developed that displayed selective detection of iodide ions in the presence of interferences. Sensors displayed the fluorescence emission enhancement response toward I^- with detection limits of 8.0 and 11.0 nM, respectively, which is accomplished through inhibition of intramolecular charge transfer and C=N isomerization. Excellent sensitivity and unique fluorescence enhancement response of sensors toward I^- make them superior because most of the previously reported iodide sensors are based on the fluorescence quenching mechanism and are less sensitive. The sensing potential of sensors toward I^- ions was investigated through ¹H NMR titration, dynamic light scattering, Job's plots, and density functional theory analysis. Further, sensors displayed reversible behavior by the alternate addition of I^- and Cu²⁺ ions that substantiate their role as recyclable sensors for the on-site detection of I^- ions. Advantageously, fluorescence enhancement response of sensors was favorably used for fluorescence imaging of I^- in live HeLa cells and the design of the logic gate. These sensors were successfully applied in diversified applications such as the preparation of sensors' coated paper strips and the determination of I^- ions in blood serum, food, and real water samples.

Fluorene-Based Fluorometric and Colorimetric Conjugated Polymers for Sensitive Detection of 2,4,6-Trinitrophenol Explosive in Aqueous Medium

Nitroaromatic explosives are a class of compounds that are responsible for various health hazards and terrorist outrages. Among these, sensitive detection of 2,4,6-trinitrophenol (TNP) explosive has always been highly desirable considering public health and national security. In this regard, three fluorene-based conjugated polymers (CP 1, CP 2, and CP 3) were synthesized through the Suzuki-Miyaura coupling reaction and were found to be highly sensitive for fluorescence detection of TNP with detection limits of 3.2, 5.7, and 6.1 pM, respectively. Excellent selectivity of CPs toward TNP was attributed to their unique π-π interactions based on fluorescence studies and density functional theory (DFT) calculations. The high sensitivity of CPs to TNP was attributed to the static quenching mechanism based on the photoinduced electron transfer process and was evaluated by fluorescence, UV-visible absorption, dynamic light scattering, Job's plots, the Benesi-Hildebrand plots, and DFT calculations. CPs were also used for colorimetric and real-water sample analysis for the detection of TNP explosive. Meanwhile, sensor-coated test strips were fabricated for on-site detection of TNP, which makes them convenient solid-supported sensors.

Impact of alien fishes on the distribution pattern of indigenous freshwater fishes of Punjab, Pakistan

Pakistan is the country with mega freshwater fish diversity of native and alien species. In the presence of enormous native fishes varies species of exotic fishes have been introduced into the freshwater bodies of Pakistan which are competing with native freshwater fish fauna and making them deprive of food and habitat as well. Intentional or accidental introductions of animals, plants and pathogens away from their native niche is considered as major leading problem for biodiversity of invaded habitat. Three years study (from January 2017 to December 2019) was conducted in freshwater bodies of Province Punjab, Pakistan. Study was designed to know exotic species impacts on the distribution of native species of fishes. During current survey a total of 68 (indigenous and exotic) fish species belonging to 14 families were recorded from head Qadirabad, head Baloki, Islam headworks and Rasul barrage. Statistical analysis showed that Shannon-Wiener diversity index was the highest (1.41) at both Rasul barrage and Islam headworks but, invasive species were present in very less number in these study sites i.e. Oreochromis mozambicus, O. niloticus, Hypophthalmichthys nobilis, Carassius auratus, Ctenophryngdon idella, Cyprinus carpio and H. molitrix. The diversity index showed that comparatively low diversity was present in both area head Qadirabad (1.30) and head Baloki (1.4) due to high pressure of invasive species. Direct observation of species and statistical analysis showed that aliens' species produced negative impact on the local fish fauna diversity, evenness, and numbers. It is concluded that many factors are impacts on the diversity of native fishes, but alien (invasive) species also play a major role to reduction of native species, because aliens' species produce competition for native species. So it is urgent need to analysis the aliens and native food web and roosting sites in Pakistan, in future.