Concentration-dependent Fluorescence Research Articles

Aptamer-Loop DNA Nanoflower Recognition and Multicolor Fluorescent Carbon Quantum Dots Labeling System for Multitarget Living Cell Imaging.

Visualization of multiple targets in living cells is important for understanding complex biological processes, but it still faces difficulties, such as complex operation, difficulty in multiplexing, and expensive equipment. Here, we developed a nanoplatform integrating a nucleic acid aptamer and DNA nanotechnology for living cell imaging. Aptamer-based recognition probes (RPs) were synthesized through rolling circle amplification, which were further self-assembled into DNA nanoflowers encapsulated by an aptamer loop. The signal probes (SPs) were obtained by conjugation of multicolor emission carbon quantum dots with oligonucleotides complementary to RPs. Through base pairing, RPs and SPs were hybridized to generate aptamer sgc8-, AS1411-, and Apt-based imaging systems. They were used for individual/simultaneous imaging of cellular membrane protein PTK7, nucleolin, and adenosine triphosphate (ATP) molecules. Fluorescence imaging and intensity analysis showed that the living cell imaging system can not only specifically recognize and efficiently bind their respective targets but also provide a 5-10-fold signal amplification. Cell-cycle-dependent distribution of nucleolin and concentration-dependent fluorescence intensity of ATP demonstrated the utility of the system for tracking changes in cellular status. Overall, this system shows the potential to be a simple, low-cost, highly selective, and sensitive living cell imaging platform.

Spectrofluorometric determination of calcium in the human nasal secretions investigating the association with olfactory function

Ionic microenvironment of the nasal secretions especially calcium ions play essential role in the olfactory transmission. However, there is a critical need to determine the free calcium levels in healthy people's nasal secretions in contrast to those of patients with olfactory impairment. A selective spectrofluorometric method was created to quantify nasal calcium levels utilizing its quenching ability to the fluorescence of the functionalized carbon quantum dots. The surface of carbon quantum dots was functionalized with calcium ionophore A23187 and ion association complex, calcium phosphotungstate, to improve the selectively to quantify calcium ions. The functionalized carbon quantum dots exhibited a concentration-dependent fluorescence quenching upon interaction with calcium ions. Different factors influencing the quenching process were done to provide efficient analytical process. The new method, demonstrated accurate calcium determination over the concentration range of 200–4000 ng/mL. The suggested technique was used to measure the calcium in the nasal secretions of both healthy people and patients with olfactory impairment. The findings revealed significantly higher calcium levels in the patient with olfactory dysfunction (healthy vs. patient; 735 ± 20 ng/mL vs. 2987 ± 37 ng/mL, p < 0.05).

Aggregation-induced-emission red carbon dots for ratiometric sensing of norfloxacin and anti-counterfeiting

The detection of trace antibiotic residues holds significant importance because it’s related to food safety and human health. In this study, we developed a new high-yield red-emitting carbon dots (R-CDs) with aggregation-induced emission properties for ratiometric sensing of norfloxacin. R-CDs were prepared in 30 min using an economical and efficient microwave-assisted method with tartaric acid and o-phenylenediamine as precursors, achieving a high yield of 34.4 %. R-CDs showed concentration-dependent fluorescence and aggregation-induced-emission properties. A ratiometric fluorescent probe for detecting the norfloxacin was developed. In the range of 0–40 μM, the intensity ratio of two emission peaks (I445 nm/I395 nm) towards norfloxacin show good linear relationship with its concentrations and a low detection limit was obtained (36.78 nM). In addition, complex patterns were developed for anti-counterfeiting based on different emission phenomenon at different concentrations. In summary, this study designed a novel ratiometric fluorescent probe for detection of norfloxacin, which greatly shortens the detection time and improves efficiency compared with high-performance liquid chromatography and other methods. The study will promote the application of carbon dots in anti-counterfeiting and other related fields, laying the foundation for the preparation of low-cost photosensitive anti-counterfeiting materials.

Fluorometric and Colorimetric Method for SARS-CoV-2 Detection Using Designed Aptamer Display Particles.

SARS-CoV-2, the virus responsible for the COVID-19 pandemic, has spurred the urgent need for practical diagnostics with high sensitivity and selectivity. Although advanced diagnostic tools have emerged to efficiently control pandemics, they still have costly limitations owing to their reliance on antibodies or enzymes and require high-tech equipment. Therefore, there is still a need to develop rapid and low-cost diagnostics with high sensitivity and selectivity. In this study, we generated aptamer display particles (AdP), enabling easy fabrication of a SARS-CoV-2 detection matrix through particle PCR, and applied it to diagnosis using fluorometric and colorimetric assays. We designed two AdPs, C1-AdP and C4-AdP, displayed with SpS1-C1 and SpS1-C4 aptamers, respectively, and showed their high binding ability against SARS-CoV-2 spike protein with a concentration-dependent fluorescence increase. This enabled detection even at low concentrations (0.5 nM). To validate its use as a diagnostic tool for SARS-CoV-2, we designed a sandwich-type assay using two AdPs and high-quality aptamers targeting SARS-CoV-2 pseudoviruses. The fluorometric assay achieved a detection limit of 3.9 × 103 pseudoviruses/mL. The colorimetric assay using an amplification approach exhibited higher sensitivity, with a detection limit of 1 × 101 pseudoviruses/mL, and a broad range of over four orders of magnitude was observed.

Excitation Wavelength and Concentration Dependent Photophysical behaviour of Dipolar Molecular rotors in Solution: Role of Structural Modification

The present work demonstrates that the twisted intramolecular charge transfer (TICT) and Intramolecular charge transfer (ICT) process can be achieved by structural modification of a molecule. The DMMC (2-(4-(dimethylamino)benzylidene)malononitrile) and DMDC (2-(4-(dimethylamino)benzylidene)malononitrile) exhibit TICT and ICT state respectively via structural modification at the ground state. Solvent-dependent fluorescence enhancement of these molecules is monitored by comparing the relative intensity of locally excited (LE) and ICT emission band from excitation wavelength and concentration-dependent study.Both molecules display the ICT emission process at excited state depending upon excitation wavelength and concentration in solution. Interestingly, aggregation behaviour is also observed during excitation wavelength and concentration-dependent study in H2O. Solvent and excitation wavelength-dependent quenching and enhancement of fluorescence properties are also observed. Dipolar state and molecular orientation may play an important role in excitation and concentration-dependent fluorescence process in solution.

Water sensitive fluorescence tuning of V-shaped ESIPT fluorophores: Substituent effect and trace amount water sensing in DMSO

Highly sensitive nature of excited state intramolecular proton transfer (ESIPT) functionality in organic fluorophores made them potential candidates for developing environmental sensors and bioimaging applications. Herein, we report the synthesis of V-shaped Dapsone based Schiff base ESIPT derivatives (1–3) and water sensitive wide fluorescence tuning from blue to red in DMSO. Solid-state structural analysis confirmed the V-shaped molecular structure with intramolecular H-bonding and substituent dependent molecular packing in the crystal lattice. 1 showed strong solid-state fluorescence (λmax = 554 nm, Φf = 21.2 %) whereas methoxy substitution (2 and 3) produced tunable but significantly reduced fluorescence (λmax = 547 (2) and 615 nm (3), Φf = 2.1 (2) and 6.5 % (3)). Interestingly, aggregation induced emission (AIE) studies in DMSO-water mixture revealed water sensitive fluorescence tuning. The trace amount of water (less than 1 %) in DMSO converted the non-emissive 1–3 into highly emissive state due to keto tautomer formation. Further increasing water percentage produced deprotonated state of 1–3 in DMSO and enhanced the fluorescence intensity with red shifting of emission peak. At higher water fraction, 1–3 in DMSO produced aggregates and red shifted the emission with reduction of fluorescence intensity. The concentration dependent fluorescence study revealed the very low detection limit of water in DMSO. The limit of detection (LOD) of 1, 2 and 3 were 0.14, 1.04 and 0.65 % of water in DMSO. Hence, simple Schiff bases of 1–3 showed water concentration dependent keto isomer, deprotonated and aggregated state tunable fluorescence in DMSO. Further, scanning electron microscopic (SEM) studies of 1–3 showed water concentration controlled self-assembly and tunable fluorescence.

A fluorescence chemo sensor approach for determination of finerenone in pharmaceutical formulation and human plasma: Method development and validation

Finerenone, a non-steroidal mineralocorticoid receptor antagonist, has gained recent approval for treating cardiovascular and kidney-related conditions. Herein, an innovative fluorescence chemo sensor was developed for the determination of finerenone in the pharmaceutical dosage form and the plasma matrix. The method is basically based on chemical transformation of finerenone into a fluorescent product through sequential reactions. This transformation occurs through a sequence of steps involving the interaction of finerenone with trimethylamine, resulting in the formation of a nucleophilic intermediate that subsequently reacts with bromoacetyl bromide to form fluorescent product, (S)-N-(2-bromoacetyl)-4-(4-cyano-2-methoxyphenyl)-5-ethoxy-2,8-dimethyl-1,4-dihydro-1,6-naphthyridine-3-carboxamide. The formed fluorescent product exhibits defined emission peak at 338 nm when excited at 248 nm. Significant concentration-dependent fluorescence enhancement was obtained enabling precise finerenone determination in the pharmaceutical formulation and plasma matrix. The method was optimized and validated providing sensitive determination over linearity range of 1–200 ng/mL with a lower limit of detection at 0.280 ng/mL. This strategy provides an efficient, economical substitute and straightforward, more sensitive analytical method for finerenone assessment in various matrices, in contrast to the previously published method, high-performance liquid chromatography-tandem mass spectrometry, which is expensive and time-consuming.

Luminescence properties and Judd-Ofelt analysis of Tb3+ doped Sr2YTaO6 double perovskite phosphors for white LED applications.

A series of Tb3+-doped Sr2YTaO6 double perovskite phosphors (SYT:Tb3+) were synthesized using a conventional solid-state reaction method. A strong green emission was observed in the SYT:Tb3+ phosphors, and the optimal doping concentration of Tb3+ was confirmed to be 5 mol%. The electric dipole-dipole interaction was ascribed to be the main mechanism for the luminescence concentration quenching. Analysis of the concentration-dependent fluorescence decay confirmed that the self-generated quenching model holds for the dynamic process of Tb3+ decays in SYT. Furthermore, the internal quantum efficiencies, non-radiative transition rates, and energy transfer rates of the 5D4 level for the SYT:Tb3+ samples were estimated, respectively. The luminescence thermal stability of the sample was also evaluated based on the Arrhenius model. The chromaticity shift of the SYT:5 mol% Tb3+ phosphor was examined to be 0.013 when the sample temperature was increased from 303 to 483 K, thus indicating excellent chromaticity shifting resistance under high temperature conditions. Moreover, the Judd-Ofelt parameters were calculated from the emission spectra of SYT:Tb3+ to be Ω2 = 0.29 × 10-20, Ω4 = 0.45 × 10-20, and Ω6 = 0.72 × 10-20 cm2, respectively. The fluorescence branching ratios and radiative transition rates for the 5D4 level were calculated based on the obtained Judd-Ofelt parameters. Finally, a white light-emitting diode (LED) prototype was assembled using a 310 nm LED chip combined with a prepared green SYT:Tb3+ phosphor and two other commercial blue and red phosphors. The obtained warm white light exhibits good chromaticity coordinates (0.32, 0.32) and a high color rendering index of 96.1. Based on the above results, it can be known that the prepared SYT:Tb3+ phosphors have a potential application as green emitting phosphors in white LEDs.

Tracking and recording of intracellular oxygen concentration changes in cell organelles: preparation and function of azide-modified fluorescent probes.

Tracking hypoxic environments and changes in oxygen levels contribute to the elucidation of pathological mechanisms. In this study, we attempted to design molecular probes that can be activated to show fluorescence under hypoxic conditions and that can move to specific cell organelles. Considering that azide groups were selectively reduced to primary amines by reductases under hypoxic conditions, we prepared Hoechst and fluorophore Cy-5 derivatives with azide groups (Hoechst-N3 and Cy-N3) as hypoxia probes. Hoechst-N3 and Cy-N3 showed weak fluorescence, but once activated in the cytosol of hypoxic cells, they exhibited robust fluorescence and then moved to their target organelles, the cell nucleus and mitochondria. In addition, when these probes were administered to the cells in the proper sequence, each probe was activated in response to the intracellular oxygen concentration at that point and exhibited oxygen concentration-dependent fluorescence at the target organelle. By measuring the fluorescence intensity of the cell nucleus and mitochondria, we successfully traced the history of changes in intracellular oxygen levels. Thus, we achieved tracking and recording of oxygen status in the cells.

Cadmium selenium quantum dot based nanosensor with femto molar level sensitivity for the detection of the pesticide endosulfan

Endosulfan (6,7,8,9,10,10-Hexachloro-1,5,5a,6,9,9a-hexahydro-6,9-methano-2,4,3-benzodioxathiepine-3-oxide) is an off-patent insecticide used in agricultural farms. Its usage as a pesticide has become highly controversial over the last few decades. This is due to its reported hazardous nature to health and side effects like growth retardation, hydrocephalus, and undesired changes in the male and female hormones leading to complications in sexual maturity. Endosulfan is the main culprit among all pesticide poisoning incidents around the world. Though the usage of this dreaded pesticide is banned by most countries, the high stability of this molecule to withstand degradation for a long period poses a threat to mankind even today. So, it has become highly essential to detect the presence of this poisonous pesticide in the drinking water and milk around these places. It is also advisable to check the presence of this toxic material in the blood of the population living in and around these places so that an early and appropriate management strategy can be adopted. With this aim, we have developed a sensor for endosulfan that displayed high selectivity and sensitivity among all other common analytes in water and biological samples, with a wide linear concentration range (2 fM to 2 mM), a low detection limit (2 fM), and rapid response. A citrate-functionalized cadmium-selenium quantum dot was used for this purpose, which showed a concentration-dependent fluorescence enhancement, enabling easy and sensitive sensing. This sensor was utilized to detect endosulfan in different sources of water, human blood serum, and milk samples with good recoveries. It is also noted that the quantum dot forms a stable complex with endosulfan and is easy to separate from the contaminated source, paving the way for purifying the contaminated water. More detailed tests and validation of the sensor are needed to confirm these observations.

Development of fluorescence chemo sensor for selective histamine determination in spiked human plasma samples

Histamine is crucial for controlling a variety of physiological processes and its dysregulation is linked to various pathological conditions, including allergic disorders, autoimmune diseases and inflammatory conditions. Herein, a novel fluorescence chemo sensor was produced to measure histamine in the pure form and spiked human plasma matrix. The proposed method is based on chemical transformation of histamine into a fluorescent product, N-(2-(1H-imidazol-4-yl) ethyl)-2-bromoacetamide, exhibiting unique fluorescence properties compared to non-fluorescent histamine molecule. This transformation occurs through a sequence of chemical reactions involving the interaction of histamine with trimethylamine, resulting in the formation of a nucleophilic intermediate that subsequently reacts with electrophilic bromoacetyl bromide. The transformed fluorescent product demonstrates an emission at 340 nm after being excited at 250 nm. Significant concentration-dependent fluorescence enhancement was obtained enabling histamine determination. The procedures were examined for accuracy, precision, selectivity, and robustness in line with the ICH M10 recommendations. The method exhibits a lower limit of quantification at 0.25 ng/mL and dynamic detection throughout a linearity range of 1–200 ng/mL, providing accurate assessment of histamine in the plasma matrix.

Mechanochromism, tunable pure organic room temperature phosphorescence, single-molecule near-white emission, digital encryption, and anti-counterfeiting

The development of tunable pure organic room temperature phosphorescence and single-molecule white light emitters still faces a great challenge due to ineffective intersystem crossing and sensitive triplet excitons. Here, two phenothiazine based luminogens named PtzIP and PtzIPCN were designed and synthesized. PtzIP exhibits mechanochromic activity with hypsochromic shift of 25 nm, tunable room temperature phosphorescence from 613 nm to 530 nm and 560 nm, then to 540 nm and 585 nm by crushing and grinding, and single-molecule near-white light emission with the (CIE: Commission International de I'Eclairage) CIE coordinates of (0.33, 0.25), but PtzIPCN shows mechanochromism and room temperature phosphorescence inertness in crystalline state. By choosing polymethyl methacrylate (PMMA) and 4-fluorobenzophenone(F-BP) as host materials, as well PtzIP and PtzIPCN as guest materials, a series of host-guest doping systems were constructed and optimized by tuning doping ratio. PtzIP/PMMA and PtzIPCN/PMMA doping systems present concentration dependent fluorescence and phosphorescence emission, and RTP lifetime and afterglow of PtzIPCN/PMMA are up to 185.31 ms of 2.0 s. Furthermore, the lifetime of F-BP/PtzIPCN increases to 216.63 ms at doping ratio of 1:1000 for F-BP and PtzIPCN. Based on different luminescent properties of PtzIP and PtzIPCN in the doping systems, a series of high-level digital encryption and anti-counterfeiting patterns were successfully constructed. More importantly, the underlying mechanism behind luminescent properties were explored in detail by photophysical testing, crystal analysis, and theoretical calculations.

Green production of tunable multicolor nanoparticles with diamond structure from long-flame coal by a one-step mild oxidation

The complex compositions and structural features of low-rank coal obstruct its wide use in materials applications directly. Graphene nanocarbon hydrosol with uniform particle size and containing nanodiamond structures were prepared from long-flame coal by a simple H2O2 oxidation, achieving the highest extraction rate of 30.86%, and the depolymerization degree was 80.21% when the temperature was 80 °C. The average diameter of the carbon nanoparticles was 1.86 ± 0.62 nm with 2–3 graphite flake layers, and these graphite flake layers were derived from the stable crystalline domains in the raw coal. Carbon nanoparticles exhibited good excitation wavelength-dependent and concentration-dependent fluorescence, which can be tunable from blue to green fluorescence by adjusting the concentration (0.19–1.5 g/L) and excitation wavelength (340–460 nm), the reason may be due to the combined effect of the relative intensity changes of various types of oxygenous groups, low-lying effects resulting from n(OH)→π*(CO) interactions between the hydroxyl groups and carbonyl groups, and the aggregation of particle. The post-reaction residue has a similar structural composition to that of humic acid and could be used for developing functional materials and agricultural restoration. Therefore, preparing carbon nanoparticles and humic acid by mild oxidation of hydrogen peroxide for the high-value utilization of long-flame coal has good application prospects.

Novel spectrofluorometric method utilizing functionalized carbon quantum dots for determining histamine levels in nasal secretions: Implications for allergic rhinitis

Histamine plays a crucial role in regulating various physiological functions and is significantly involved in the development of allergic rhinitis. Accurately measuring histamine levels in nasal secretions can serve as a specific indicator for studying mast cell activation and diagnosing allergic reactions. However, the controversy surrounding histamine levels in nasal secretions during allergenic stimulation suggests potential inaccuracies and imprecision in the analytical methods used, as well as the presence of substances that may interfere with the determination of histamine. In this study, a sensitive and selective spectrofluorometric method was developed using carbon quantum dots (CQDs) derived from beetroot slices, which are non-toxic and eco-friendly materials. These CQDs were functionalized with histamine tetra phenyl borate to determine histamine levels in nasal secretions. Various characterization techniques were employed to confirm the successful synthesis and functionalization of the CQDs. The functionalized CQDs demonstrated enhanced fluorescence and selective interaction with histamine, leading to concentration-dependent fluorescence quenching. The developed method was successfully utilized to compare histamine levels in nasal secretions of healthy individuals and patients with allergic rhinitis. The results showed that the histamine level was significantly higher in patients with allergic rhinitis than in healthy individuals, suggesting a potential association between allergic rhinitis and histamine, (normal vs. patient: 350 ± 20 ng/mL vs. 2520 ± 37 ng/mL, p < 0.05). Furthermore, the proposed spectrofluorometric method exhibited improved linearity range, dynamic range, and detection limit compared to a previously reported spectrophotometric method.

Designing Nonconventional Luminescent Materials with Efficient Emission in Dilute Solutions via Modulation of Dynamic Hydrogen Bonds.

Nonconventional luminescent materials (NLMs) which do not contain traditional aromatic chromophores are of great interest due to their unique chemical structures, optical properties, and their potential applications in various areas, such as cellular imaging and chemical sensing. However, most reported NLMs show weak or no emission in dilute solutions, which severely limits their applications. In this work, dynamic hydrogen bonds were utilized to design NLMs with efficient emission in dilute solutions. To further validate the results, polymers P1 and P2 were successfully prepared and investigated. It was found that the luminescence quantum efficiency of P1 and P2 at a concentration of 0.1 mg/mL in water solution was 8.9 and 0.6%, respectively. The high efficiency can be attributed to the fact that polymer P1 has more intra- or intermolecular dynamic hydrogen bonds and other short interactions than P2 in dilute solutions, allowing P1 to achieve the through-space conjugation effect to increase the degree of system conjugation, restrict molecular motion, and decrease nonradiative transitions, which can effectively improve luminescence. In addition, polymer P2 exhibits the characteristics of clustering-triggered emission, excitation wavelength-dependent and concentration-dependent fluorescence properties, excellent photobleaching resistance, low cytotoxicity, and selective recognition of Fe3+. The present study investigates the manipulation of luminescence properties of NLMs in dilute solutions through the modulation of dynamic hydrogen bonds. This approach can serve as a semi-empirical technique for designing and building innovative NLMs in the times ahead.

Rational design of a ratiometric fluorescent probe for imaging lysosomal nitroreductase activity

Overexpressed nitroreductase (NTR) is often utilized to evaluate the hypoxic degree in tumor tissues, thus it is of great importance to develop high selective and efficient optical method to detect NTR. The dynamic fusion and function of lysosome promoted us to explore the possible appearance of NTR inside this organelle and to probe its behavior in a cellular context. In this work, a ratiometric fluorescent probe based on an extended π-π conjugation of a triphenylamine unit was designed for NTR detection and lysosomes imaging. The dual-emission mechanism of the probe in the presence of catalytic NTR was confirmed by theoretical study. The structure–function relationship between probe and NTR was revealed by docking calculations, suggesting a suitable structural and spatial match of them. The photophysical studies showed the probe had high selectivity, rapid response and a wide pH range towards NTR. MTT assay indicated the probe had low cytotoxicity in both normal (HUVEC) and tumor (MCF-7) cells. Furthermore, the inverse fluorescent imaging results confirmed the probe was NTR-active and exhibited time- and concentration-dependent fluorescence signals. In addition, the relatively high Pearson’s correlation coefficient (0.99 in HepG2 and 0.97 in MCF-7 cells, compared to Lyso-Tracker Red) demonstrated the probe had excellent lysosomes colocalization. This study illustrates a ratiometric detection of NTR agent for lysosomes fluorescent imaging, which may provide a novel insight in molecular design.

A New Insight into the Singlet Oxygen Mechanism for Photodynamic Therapy.

Modern photodynamic therapy has been built on the mechanism of the interaction between the photosensitizer (porphyrin derivatives) and oxygen to produce singlet oxygen, which relies on energy transfer from the triplet excited state (T1) of porphyrin to the excited state of oxygen. In this process, the energy transfer from the singlet excited state (S1) of porphyrin to oxygen is believed to be not pronounced as the rapid decay of S1 and the large energy mismatch. Here, we have evidenced the existence of an energy transfer between S1 and oxygen, which can contribute to the production of singlet oxygen. For hematoporphyrin monomethyl ether (HMME), the Stern-Volmer constant of S1 (KSV') is 0.023 kPa-1, according to the oxygen concentration-dependent steady fluorescence intensities. In addition, fluorescence dynamic curves of S1 under various oxygen concentrations have also been measured through ultrafast pump probe experiments to further verify our results.

Surficial amino groups coupling induced concentration-dependent fluorescence and fluorescence quantum yield of nitrogen-dopped carbon quantum dots via efficient charge transfer.

Modification of surficial functional groups among carbon quantum dots (CQDs) has been considered an efficient approach to regulate the fluorescence emission of CQDs. However, the mechanism of how surficial functional groups affect fluorescence is vague which fundamentally limits the further applications of CQDs. Here we report the concentration-dependent fluorescence and fluorescence quantum yield of nitrogen-dopped carbon quantum dots (N-CQDs). At high concentrations (≥0.188g/L), fluorescence redshift occurs accompanied with decrease in fluorescence quantum yield. Fluorescence excitation spectra and HOMO-LUMO energy gaps calculations show that energy levels of excited states of N-CQDs are relocated via the coupling of surficial amino groups among N-CQDs. Furthermore, electron density difference maps and broadened fluorescence spectra obtained from both experimental measurement and theoretical calculation further confirm that the coupling of surficial amino groups dominates the fluorescence property and verify the formation of charge-transfer state of N-CQDs complex at high concentrations which provides pathways for efficient charge transfer. Given that charge-transfer state induced fluorescence loss and fluorescence spectra broadening are the typical characteristics of organic molecules, CQDs exhibit the optical properties of both quantum dots and organic molecules.

Use of Ag-Au-ICG to increase fluorescence image of human hepatocellular carcinoma cell lines

Indocyanine green (ICG) is effective for a variety of applications including liver tumour imaging and operates in the near-infrared window. Agents for near-infrared imaging are, however, still in clinical development. The present study aimed to prepare and investigate fluorescence emission properties of ICG in combination with Ag-Au in order to enhance their specific interactions with human hepatocellular carcinoma cell lines (HepG-2). The Ag-Au-ICG complex was prepared via physical adsorption, and hence evaluated for fluorescence spectra using a spectrophotometer. Ag-Au-ICG at an optimised dosage (Ag-Au:ICG = 0.0147:1 molar ratio) in Intralipid medium was added to HepG-2 to observe the maximum fluorescence signal intensity, which further enhanced HepG-2 contrast fluorescence. Ag-Au-ICG served as a fluorescence enhancer bound onto the liposome membrane, whilst free Ag, Au, and pure ICG induced low levels of cytotoxicity in HepG-2 and a normal human cell line. Thus, our findings provided new insights for the liver cancer imaging. Highlights Concentration-dependent fluorescence peaking in the near-infrared window revealed ICG aggregation in Ag-Au molecules. Ag-Au-ICG fluorescence intensity depended strongly on the environmental media. Human hepatocellular carcinoma cell lines treated with Ag-Au-ICG in Intralipid enhanced the contrast of fluorescence microscopy images by decreasing the level of scattering in the cell lines with the contrast values being approximately five times those observed in pure ICG in Intralipid.

Dual-Mode Multiple Ion Sensing via Analyte-Specific Modulation of Keto-Enol Tautomerization of an ESIPT Active Pyrene Derivative: Experimental Findings and Computational Rationalization.

A pyrene-based e xcited - state intramolecular proton transfer (ESIPT) active probe PMHMP was synthesized, characterized, and employed for the ppb-level, dual-mode, and high-fidelity detection of Cu2+ (LOD: 7.8 ppb) and Zn2+ ions (LOD: 4.2 ppb) in acetonitrile medium. The colorless solution of PMHMP turned yellow upon the addition of Cu2+, suggesting its ratiometric, naked-eye sensing. On the contrary, Zn2+ ions displayed concentration-dependent fluorescence rise till a 0.5 mole fraction and subsequent quenching. Mechanistic investigations indicated the formation of a 1:2 exciplex (Zn2+:PMHMP) at a lower concentration of Zn2+, which eventually turned into a more stable 1:1 (Zn2+:PMHMP) complex with an additional amount of Zn2+ ions. However, in both cases, it was observed that the hydroxyl group and the nitrogen atom of the azomethine unit were involved in the metal ion coordination, which eventually altered the ESIPT emission. Furthermore, a green-fluorescent 2:1 PMHMP-Zn2+ complex was developed and additionally employed for the fluorimetric analysis of both Cu2+ and H2PO4 - ions. The Cu2+ ion, owing to its higher binding affinity for PMHMP, could replace the Zn2+ ion from the preformed complex. On the other hand, H2PO4 - formed a tertiary adduct with the Zn2+-complex, leading to a distinguishable optical signal. Furthermore, extensive and organized density functional theory calculations were performed to explore the ESIPT behavior of PMHMP and the geometrical and electronic properties of the metal complexes.