Bioimaging Studies Research Articles

Single-walled carbon nanotube membranes as non-reflective substrates for nanophotonic applications

We demonstrate that single-walled carbon nanotube (SWCNT) membranes can be successfully utilized as nanometer-thick substrates for enhanced visualization and facilitated study of individual nanoparticles. As model objects, we transfer optically resonant 200 nm silicon nanoparticles onto pristine and ethanol-densified SWCNT membranes by the femtosecond laser printing method. We image nanoparticles by scanning electron and bright-field optical microscopy, and characterize by linear and Raman scattering spectroscopy. The use of a pristine SWCNT membrane allows to achieve an order-of-magnitude enhancement of the optical contrast of the nanoparticle bright field image over the results shown in the case of the glass substrate use. The observed optical contrast enhancement is in agreement with the spectrophotometric measurements showing an extremely low specular reflectance of the pristine membrane (≤0.1%). Owing to the high transparency, negligibly small reflectance and thickness, SWCNT membranes offer a variety of perspective applications in nanophotonics, bioimaging and synchrotron radiation studies.

Simple Colorimetric and Fluorescence Chemosensing Probe for Selective Detection of Sn2+ Ions in an Aqueous Solution: Evaluation of the Novel Sensing Mechanism and Its Bioimaging Applications.

An easily accessible colorimetric and fluorescence probe 4-((3-chloro-1,4-dioxo-1,4-dihydronaphthalen-2-yl)amino)benzenesulfonamide (4CBS) was successfully developed for the selective and sensitive detection of Sn2+ in an aqueous solution. The sensing mechanism involves reduction of -C═O into -C-OH groups in 4CBS upon the addition of Sn2+, which initiates the fluorescence turn-on mode. A better linear relationship was achieved between fluorescence intensity and Sn2+ concentration in the range of 0-62.5 μM, with a detection limit (LOD) of 0.115 μM. The binding mechanism of 4CBS for Sn2+ was confirmed by Fourier transform infrared analysis, NMR titrations, and mass (electrospray ionization) spectral analysis. Likewise, the proposed sensing mechanism was supported by quantum chemical calculations. Moreover, bioimaging studies demonstrated that the chemosensing probe 4CBS is an effective fluorescent marker for the detection of Sn2+ in living cells and zebrafish. Significantly, 4CBS was able to discriminate between Sn2+ in human cancer cells and Sn2+ in normal live cells.

Trace Quantity Detection of H2PO4– by Fluorescent Metal–Organic Framework (F-MOF) and Bioimaging Study

Drinking water quality management and sustainable environment to water bodies are a major concern to Public Health Engineering departments. Inorganic Phosphate (Pi), one of the major inorganic pollutants, is addressed for the last two decades regarding trace quantity detection. Over the past few years, a large number of fluorescent metal-organic frameworks (F-MOFs) have been studied to explore the desirable method for selective water analysis. In this article, a Zn(II) 3D F-MOF, {[Zn2(PCDF-INH)(BDC)2].(H2O)}n (1) (H2BDC = 1,4-Benzenedicarboxylic acid, and PCDF–INH = N, Nʹ-diisonicotinoyl-2-hydroxy-5-methyl-isophthalaldehyde dihydrazone) is used for selective recognition of H2PO4− anion by ‘turn-off’ fluorescent sensing technique. Single-crystal X-ray analysis accounts that the asymmetric unit is constituted of two different Zn(II) centres by PCDF–INH and the bridging group, BDC2− ions are responsible for the generation of helical polymer and the biporous structures (14.807×13.096 A2 and 24.905×24.932 A2). The compound, 1, exhibits strong emission at 505 nm in CH3OH-H2O solution and is 'turn-off' upon the addition of H2PO4−. The selectivity and specificity for H2PO4− have been checked in the presence of fifteen different anions including different phosphates (PO43−, HPO42−, P2O74−). The entire sensing activity of 1 is examined by spectrofluorometric method, 1H–NMR titration, PXRD analysis, bio-imaging study, and the limit of detection is 3.903 μM. However, in vitro bio-sensing analysis confers that F-MOF (1) is sensible toward the H2PO4− ion at a trace level in the human lung fibroblast cells and human liver cancer cell line Hep G2.

Detection of nickel by chemo and fluoro sensing technologies.

Sensing technology for heavy metal detection is very crucial for recent decades as the detection method is very easy, rapid, and does not require any pre-treatment of the sample. Nickel is a trace element in the human body and basically a moderate toxic element. There is a limited number of chemo and fluoro sensors reported for nickel as compared to other transition metal ion. Therefore, there is a need for the detailed structure and property studies of the nickel-probes as the knowledge can help in the upcoming development of probes for the nickel. In this review, we have discussed about different colorimetric, fluorimetric and fluorescent chemosensor and their structure, characterization, detection limit, association constant, media, and bio-imaging studies if they are active.

Novel integrated sensing system of calixarene and rhodamine molecules for selective colorimetric and fluorometric detection of Hg2+ ions in living cells.

Three novel and facile calixarene derivatives (5, 6 and 7), which were appended with four rhodamine units at the upper rim of calixarene skeleton, were firstly prepared and evaluated for selective detection of metal ions in solution. Receptors (5) and (7) indicated immediate turn on fluorescence output toward Hg2+ ions over other most competitive metal ions with the ultralow detection limits, indicating their high efficiency and reliability. The binding response to Hg2+ ions in solution was also observed through a chromogenic change (from colorless to pale pink). Furthermore, in vitro and bio-imaging studies with MCF-7 or MIA PaCa-2 cell lines were also performed to investigate the use of receptors in biological systems in order to monitor of mercury ions. Results showed that new receptors (5) or (7) were cell permeable and suitable for real-time imaging of Hg2+ in living cells (MCF-7) or (MIA PaCa-2) without any damage to healthy cell lines (HEK 293).

A Review on Schiff Base Fluorescent Chemosensors for Cell Imaging Applications.

Fluorescent determinations of analytes have proven to be a powerful method due to their simplicity, low cost, detection limit, rapid photoluminescence response, and applicability to bioimaging. Fluorescence imaging as a powerful tool for monitoring biomolecules within the living systems. Schiff base has been extensively used as strongly absorbing and colorful chromophores in the design of chemosensors. In recent years, Schiff base based fluorescent probes have been developed for the detection of various toxic analytes and imaging of various analytes in biological systems. This review gives an overview of the important fluorescent sensors which are based on Schiff base, their approaches for molecular recognition, and their potential application in bioimaging studies.

Targeted bioimaging and sensing of folate receptor-positive cancer cells using folic acid-conjugated sulfur-doped graphene quantum dots.

Forthe first time is reporteda facile in situ synthesis of folic acid-conjugated sulfur-doped graphene quantum dots (FA-SGQDs) through simple pyrolysis of citric acid (CA), 3-mercaptopropionic acid (MPA), and FA. The as-prepared FA-SGQDs were extensively characterized to confirm the synthesis and incidence of FA molecule on the surface of SGQDs through advanced characterization techniques. Upon excitation at 370-nm wavelength, FA-SGQDs exhibited blue fluorescence with an emission band at 455nm. While exhibiting relatively high quantum yield (~ 78%), favorable biocompatibility, excellent photostability, and desirable optical properties, the FA-SGQDs showed suitability as a fluorescent nanoprobe to distinguish the folate receptor (FR)-positive and FR-negative cancer cells. The experimental studies revealed that FA-SGQDs aptly entered into FR-positive cancer cells via anon-immunogenic FR-mediated endocytosis process. Additionally, the FA-SGQDs exhibited excellent free radical scavenging activity. Hence, these FA-SGQDs hold highpromise to serve as efficient fluorescent nanoprobes for the pre-diagnosis of cancer through targeted bioimaging and other pertinent biological studies. Graphical abstract.

A novel peptide-based fluorescent chemosensor for detection of zinc (II) and copper (II) through differential response and application in logic gate and bioimaging

A novel fluorescent chemosensor with dansyl-appended tetrapeptide (identified as L), was designed and synthesized using solid phase synthesis (SPPS) technology. At room temperature, L displayed high water solubility and highly selective fluorescence “turn-on” response towards Zn2+ detection in 100% aqueous solutions. Conversely, L exhibited highly selective detection of Cu2+ through fluorescence quenching by a mechanism intrinsic to the paramagnetic species. The binding stoichiometry with L and Zn2+/Cu2+ ions were determined from the Job’s plot to be 2:1, and further verified with fluorescence titration, ESI-HRMS and DFT-Calculations studies. The lowest measured detection limits for L were 13.2 nM for Zn2+ and 4.1 nM for Cu2+, respectively, with excellent sensitivity. In addition to that, L was successfully analyzed quantitatively for Zn2+ and Cu2+ ions using logic gate construction. Furthermore, L exhibited excellent cell permeation and low biotoxicity during bioimaging studies, L was able to selectively identify Zn2+ and Cu2+ ions in living LNcap cells, suggesting that the chemosensor L will be a promising biomolecular chemosensor for multifunctional detection of Zn2+ and Cu2+ through differential responses in environmental and biological systems.

Near-Infrared-Emitting Probes for Detection of Nanomolar Hydrazine in a Complete Aqueous Medium with Real-Time Application in Bioimaging and Vapor-Phase Hydrazine Detection

Hydrazine is a highly reactive inorganic compound that is commonly used as a thruster propellant in rocket fuels. In this report, the synthesis of a naphthofluorescein-based simple, sensitive, and selective colorimetric and fluorescent probe for the qualitative and quantitative determination of hydrazine is described. An ultrasensitive NIR probe is employed for the nanomolar detection of hydrazine with real-time applicability. The probe is capable of detecting hydrazine in a completely aqueous medium without the interference of other analytes. The probe reacts selectively with hydrazine and exhibits turn-on NIR emission with quantum yields ranging from Φ = 0.0011 to Φ = 0.5338. This enables the probe to selectively detect extremely low concentrations of hydrazine (∼47 nM). As a consequence, practical utility of the probe is greatly augmented. Eco-friendly test strips were prepared to monitor the hydrazine under aqueous and vapor phases. The potential of the probe was verified by monitoring the presence of hydrazine in a living system by fluorescence bioimaging studies of living cells.

Synthesis, photophysical properties and solvatochromic analysis of some naphthalene-1,8-dicarboxylic acid derivatives

Two groups of new naphthalene-1,8-dicarboxylic acid derived compounds, 6-amino-1,8-naphthalic anhydride derivatives and 2-hydroxy-6-amino-1,8-naphthalimide derivatives, have been synthesized and characterized. The spectroscopic properties of all synthesized compounds were investigated in order to be used in the field of bio-imaging studies and as intermediates for the preparation of new fluorescent bioactive compounds. Positive solvatochromism was observed from non-polar to polar solvents and it was discussed using Catalan multilinear regression analysis. Comparative study of the photophysical characteristics of naphthalic anhydride and 1,8-naphthalimide derivatives was performed. The new naphthalic anhydride 6-(4-benzyl-piperazin-1-yl)benzo[de]isochromene-1,3-dione (3) presents the highest value of fluorescence quantum yield in solvents with lower polarities. The results demonstrate that the quantum yields values of naphthalic anhydride derivatives are higher than those of naphthalimide derivatives.

Microfluidic chip enabled one-step synthesis of biofunctionalized CuInS2/ZnS quantum dots.

Biofunctionalized quantum dots (QDs) are effective target fluorescent labels for bioimaging. However, conventional synthesis of biofunctionalized I-III-VI core-shell CuInS2/ZnS QDs requires complex bench-top operations, resulting in limited product performance and variety, and is not amenable to a 'one-step' approach. In this work, we have successfully demonstrated a fully automated method for preparing denatured bovine serum albumin (dBSA)-CuInS2/ZnS QDs by introducing microfluidic (MF) chips to synthesize biofunctionalized QDs, hence establishing a 'one-step' procedure. We have also studied and optimized the reaction synthesis parameters. The emission wavelength of the dBSA-CuInS2/ZnS QDs is located in the near-infrared range and can be tuned from 650 to 750 nm by simply varying the reaction parameters. In addition, the 'one-step'-synthesized dBSA-CuInS2/ZnS QDs have a long average fluorescence lifetime of 153.76 ns and a small particle size of 5 ± 2 nm. To demonstrate the applicability of the 'one-step'-synthesized dBSA-CuInS2/ZnS QDs in bioimaging studies, we modified the QDs with folic acid and hyaluronic acid, and then performed target bioimaging and cytotoxicity tests on macrophages, liver cancer cells and pancreatic cancer cells. The cell images show that the red emission signals originate from the QDs, which indicates that the dBSA-CuInS2/ZnS QDs prepared by the MF approach are suitable optical contrast agents for target bioimaging. This 'one-step' MF-based QD synthesis approach could serve as a rapid, cost-effective, and small-scale nanocrystal production platform for complex QD formulations for a wide range of bioapplications.

Applications of Activity-Based Protein Profiling (ABPP) and Bioimaging in Drug Discovery.

Activity-based protein profiling (ABPP) and bioimaging have been developed in recent years as powerful technologies in drug discovery. Specifically, both approaches can be applied in critical steps of drug development, such as therapy target discovery, high-throughput drug screening and target identification of bioactive molecules. We have been focused on the development of various strategies that enable simultaneous activity-based protein profiling and bioimaging studies, thus facilitating an understanding of drug actions and potential toxicities. In this Minireview, we summarize these novel strategies and applications, with the aim of promoting these technologies in drug discovery.

Small Molecule as Fluorescent Probes for Monitoring Intracellular Enzymatic Transformations.

All cellular processes are the results of synchronized actions of several intracellular biochemical pathways. Recent emphasis is to visualize such pathways using appropriate small molecular reagents, dye-labeled proteins, and genetically encoded fluorescent biosensors that produce a luminescence ON response either on selective binding or on reacting with an analyte that is produced through a specific biochemical/enzymatic transformation. Studying such enzymatic processes by probing the fluorescence response as the read-out signal is expected to provide important insights into crucial biochemical transformations induced by an enzyme in its native form. Many of such studies are extended for monitoring enzymatic transformations under in vitro or in vivo condition. A few of the recent reports reveal that such molecular probes are even capable of quantifying abnormal levels of enzymes in real-time and is linked to the key area of clinical diagnostics and chemical biology. A synchronized analysis of all such reports helps in developing a rationale for designing purpose-built molecular probes or chemodosimeters as well as newer reagents for studying crucial enzymatic process or quantification of the respective enzyme. In this review, an attempt will be there to highlight several recent bioimaging reagents and studies that have provided insights into crucial biochemical or enzymatic transformations.

Recent chemo-/biosensor and bioimaging studies based on indole-decorated BODIPYs.

BODIPY is an important fluorophores due to its enhanced photophysical and chemical properties including outstanding thermal/photochemical stability, intense absorption/emission profiles, high photoluminescence quantum yield, and small Stokes' shifts. In addition to BODIPY, indole and its derivatives have recently gained attention because of their structural properties and particularly biological importance, therefore these molecules have been widely used in sensing and biosensing applications. Here, we focus on recent studies that reported the incorporation of indole-based BODIPY molecules as reporter molecules in sensing systems. We highlight the rationale for developing such systems and evaluate detection limits of the developed sensing platforms. Furthermore, we also review the application of indole-based BODIPY molecules in bioimaging studies. This article includes the evaluation of indole-based BODIPYs from synthesis to characterization and a comparison of the advantages and disadvantages of developed reporter systems, making it instructive for researchers in various disciplines for the design and development of similar systems.

A simple but efficient fluorescent sensor for ratiometric sensing of Cd2+ and bio-imaging studies

A very simple schiff base fluorescent probe (NIS) was facilely prepared via a one-step, one-pot condensation reaction between 2, 3-naphthalenediamine and imidazole-2-carboxaldehyde. Among common biologically relevant metal ions, NIS can selectively recognize Cd2+ via ratiometric fluorescence signal. The chelation of NIS with the Cd2+ ions resulted in a fluorescence enhancement together with a blue shift (˜74 nm) in the emission maxima, presumably due to the combined effects of ICT (internal charge transfer) and CHEF (chelation-enhanced fluorescence). The binding stoichiometry of NIS to Cd2+ is 1:1 and the fluorescence intensity ratio (F398/F472) changes allow a ratiometric detection of Cd2+ with the detection limit of 3.87 × 10−7 M. Under fluorescence confocal microscope and via two emission channels, the probe is capable to detect Cd2+ ions in Human liver cancer cells (SMMC-7721), zebrafish and live tissues of Arabidopsis thaliana, demonstrating its applicability for detecting Cd2+ ions in different biological context with low toxicity.

Phenothiazine-rhodamine-based colorimetric and fluorogenic 'turn-on' sensor for Zn2+ and bioimaging studies in live cells.

A phenothiazine-rhodamine (PTRH) fluorescent dyad was synthesized and its ability to selectively sense Zn2+ ions in solution and in in vitro cell lines was tested using various techniques. When compared with other competing metal ions, the PTRH probe showed the high selectivity for Zn2+ ions that was supported by electronic and emission spectral analyses. The emission band at 528nm for the PTRH probe indicated the ring closed form of PTRH, as for Zn2+ ion binding to PTRH, the λem get shift to 608nm was accompanied by a pale yellow to pink colour (under visible light) and green to pinkish red fluorescence emission (under UV light) due to ring opening of the spirolactam moiety in the PTRH ligand. Spectral overlap of the donor emission band and the absorption band of the ring opened form of the acceptor moiety contributed towards the fluorescence resonance energy transfer ON mechanism for Zn2+ ion detection. The PTRH sensor had the lowest detection limit for Zn2+ , found to be 2.89×10-8 M. The sensor also demonstrated good sensing application with minimum toxicity for in vitro analyses using HeLa cells.

Folic acid-modified ginsenoside Rg5-loaded bovine serum albumin nanoparticles for targeted cancer therapy in vitro and in vivo.

Background and purposeGinsenoside Rg5 (Rg5), a triterpene saponin, extracted from the natural herbal plant ginseng, is one of the most potent anticancer drugs against various carcinoma cells. However, the therapeutic potential of Rg5 is limited by its low solubility in water, poor bioavailability, and nontargeted delivery. Therefore, we prepared folic acid (FA)-modified bovine serum albumin (BSA) nanoparticles (FA-Rg5-BSA NPs) to improve the therapeutic efficacy and tumor targetability of Rg5.MethodsVarious aspects of the FA-Rg5-BSA NPs were characterized, including size, polydispersity, zeta potential, morphology, entrapment efficiency (EE), drug loading (DL), in vitro drug release, thermal stability, in vitro cytotoxicity, cell apoptosis, cellular uptake, in vivo antitumor effects and in vivo biodistribution imaging.ResultsThe FA-Rg5-BSA NPs showed a particle size of 201.4 nm with a polydispersity index of 0.081, uniform spherical shape, and drug loading of 12.64±4.02%. The aqueous solution of FA-Rg5-BSA NPs had favorable stability for 8 weeks at 4°C. The FA-Rg5-BSA NPs dissolved under acidic conditions. Moreover, the Rg5-BSA NPs and FA-Rg5-BSA NPs had advanced anticancer activity compared with Rg5 in MCF-7 cells, while poor cytotoxicity was observed in L929 cells. The FA-Rg5-BSA NPs facilitated cellular uptake and induced apoptosis in MCF-7 cells. In addition, in an MCF-7 xenograft mouse model, the in vivo antitumor evaluation revealed that FA-Rg5-BSA NPs were more effective in inhibiting tumor growth than Rg5 and Rg5-BSA NPs. The in vivo real-time bioimaging study showed that the FA-Rg5-BSA NPs exhibited superior tumor accumulation ability.ConclusionThe results suggested that FA-Rg5-BSA NPs could serve as a promising system to improve the antitumor effect of Rg5.

Luminescent Molecular Octopuses with a Polyhedral Oligomeric Silsesquioxane (POSS) Core and Iridium(III) Polypyridine Arms: Synthesis, Aggregation Induced Emission, Cellular Uptake, and Bioimaging Studies.

A new class of luminescent molecular hybrids in which eight cyclometalated iridium(III) polypyridine complexes are grafted onto a polyhedral oligomeric silsesquioxane (POSS) unit [POSS-{Ir(N^C)2 (py-im)}8 ](PF6 )8 [py-im=pyridine imine; HN^C=N-phenylpyrazole (Hppz) (1 a), 2-phenylpyridine (Hppy) (2 a), 2-phenylquinoline (Hpq) (3 a)] were synthesized and characterized. On photoexcitation, the complexes showed intense and long-lived orange-red to red emission in fluid solutions at room temperature and in low-temperature glasses. The photophysical properties including aggregation-induced emission and biological properties of these complexes were studied and compared with those of their POSS-free counterparts [Ir(N^C)2 (py-im)](PF6 ) [HN^C=Hppz (1 b), Hppy (2 b), Hpq (3 b)]. The (photo)cytotoxicity of the complexes was examined by the MTT assay, and their cellular uptake and intracellular localization were investigated by inductively coupled plasma-mass spectrometry and laser-scanning confocal microscopy.

Crenolanib-Derived Probes Suitable for Cell- and Tissue-Based Protein Profiling and Single-Cell Imaging.

Crenolanib (CP-868,596), a potent inhibitor of FLT3 and PDGFRα/β, is currently under phase III clinical investigation for the treatment of acute myeloid leukemia. However, the protein targets of Crenolanib in cancer cells remain obscure, which results in difficulties in understanding the mechanism of actions and side effects. To alleviate this issue, in this study, a photoaffinity probe and two fluorescent probes were created based on Crenolanib, followed by competitive protein profiling and bioimaging studies, with the aim of characterizing the cellular targets. A series of unknown protein hits, such as MAPK1, SHMT2, SLC25A11, and HIGD1A, were successfully identified by means of pull-down/LC-MS/MS; these might provide valuable clues for understanding drug action and potential toxicities. Moreover, the fluorescent probes are suitable for imaging drug distribution at the single-cell level.

Colorimetric and fluorescent sensors for the detection of Co(II), Ni(II) and Cu(II) in aqueous methanol solution

Two novel and potential Schiff base sensor compounds were synthesized by the one pot condensation method starting from 2-hydroxy-1-naphthaldehyde. Both the Schiff bases were characterized by IR, UV,1H-NMR, 13C-NMR and mass spectral studies. The cation sensing expertise of the Schiff bases was evaluated by naked eye, UV–Vis and fluorescence spectroscopic methods in aqueous methanolic medium. The cobalt(II), nickel(II) and copper(II) ions were selectively detected by both the receptors. The detection limits for the ions were found to be in the order of 10−6 M to 10−7 M. Stability constants of the complexes formed by the receptors with the three metal ions were determined by the Benesi–Hildebrand plot method. Stoichiometry of the complexes were ascertained as 1:1 (M:R) by Job’s plot method. Mode of interactions were corroborated by 1H-NMR and IR titrations. The structure of the complexes formed during the recognition process was authenticated by the ESI–mass spectroscopy method. The metal ion sensing property of the receptor is applied in bio imaging studies of human Hela cells.