Biological Imaging Applications Research Articles

Development of a ratiometric fluorescent probe with large Stokes shift and emission wavelength shift for real-time tracking of hydrazine and its multiple applications in environmental analysis and biological imaging

As a tremendously noxious and extensively utilized chemical reagent, hydrazine (N2H4) has become a serious threat to ecosystem and human health. Thus, it is desirable to exploit an efficient method for real-time tracking of hydrazine. Here, a novel ratiometric fluorescent probe PBQ-AB for hydrazine was rationally constructed from isolongifolanone. This probe displayed an extremely large Stokes shift of 230 nm and could selectively recognize hydrazine in the presence of other competitive species within an extremely short time ( 40 s). PBQ-AB also displayed some fascinating merits in the detection of hydrazine, including low detection limit (48 nM), wide pH range (5–12), excellent photostability (>240 min), and well-resolved emission wavelength shift (148 nm). Moreover, this probe was utilized to fabricate a ready-to-use electrospinning nanofibrous membrane for convenient detection of hydrazine vapor by virtue of smartphone. Furthermore, PBQ-AB was capable of determining hydrazine contaminant in environmental soil and water samples. Additionally, its favorable performance for detecting hydrazine was successfully demonstrated in live HeLa cells as well as in live Arabidopsis thaliana tissues, manifesting its promising application for labeling hydrazine in living systems. Therefore, we believed that this probe has great potential in environmental analysis and health supervision.

Removed heavy metal ions from wastewater reuse for chemiluminescence: Successive application of lignin-based composite hydrogels

The novel sulfomethylated lignin-grafted-polyacrylic acid (SL-g-PAA) hydrogel was fabricated in this work via a facile and green synthetic strategy for the efficient removal of heavy metal ions from wastewater, and then successively reused for chemiluminescence (CL). The sulfomethylation of lignin was first performed to improve its water solubility and introduce numerous active sites for adsorption of heavy metal ions. The as-synthesized SL-g-PAA hydrogel with high content of lignin exhibited the highly efficient and rapid removal of various metal ions from simulated wastewater. More importantly, the spent hydrogel (M2+@SL-g-PAA) after adsorption was reused for the first time to develop a new CL system by an ingenious strategy, in which these metal ions adsorbed on M2+@SL-g-PAA act as heterogeneous catalytic sites to catalyze the CL reaction between N-(4-aminobutyl)-N-ethylisoluminol (ABEI) and H2O2. The resultant CL system displayed high CL intensity and long duration time, which could be observed by naked eye in the dark and lasted for > 24 h. The combination of facile fabrication process, renewable raw materials, and ingenious strategy for successive application in adsorption and CL endows this lignin-based composite hydrogel with a great potential for application in wastewater treatment, biological imaging and cold light sources.

Multiphoton Photoluminescence in Hybrid Plasmon–Fiber Cavities with Au and Au@Pd Nanobipyramids: Two-Photon versus Four-Photon Processes and Rapid Quenching

We investigate the multiphoton photoluminescence (MPPL) characteristics of bare and palladium-capped gold nanobipyramid particles deposited on microfibers with diameters around 1.7 μm. A broad luminescence emission with two evident peaks is detected when the coupled gold nanobipyramid particles are illuminated with a femtosecond laser. By employing multiple peak Lorentz fitting to each PL emission spectrum and performing nonlinear order analysis of the excitation power-dependent measurement, we come to the conclusion that four-photon photoluminescence (4PPL) at around 520 nm and two-photon photoluminescence (2PPL) at longer wavelengths are the main constituents of the broad luminescence emission. Additionally, we observed unexpectedly that those two emission processes have different polarization characteristics. These characteristics can be understood and explained by taking into account the band and crystalline structure of the gold nanobipyramids. Furthermore, the L-band-related 4PPL emission is quenched for Au@Pd nanobipyramids due to the fast transfer of electrons from the gold to the palladium. This provides us with a new way of modifying the photoluminescence in coupled hybrid bimetallic nanostructures. This deeper understanding of MPPL in gold nanoparticles paves the way to precise control of the luminescence emission from plasmonic nanoparticles, which is crucial for further applications in biological imaging and photothermal therapy.

Rare-Earth Doping Graphitic Carbon Nitride Endows Distinctive Multiple Emissions with Large Stokes Shifts

Rare-Earth Doping Graphitic Carbon Nitride Endows Distinctive Multiple Emissions with Large Stokes Shifts

Synthesis and Bioapplications of Ag2 S Quantum Dots with Near-Infrared Fluorescence.

Quantum dots (QDs) with near-infrared fluorescence (NIR) are an emerging class of QDs with unique capabilities owing to the deeper tissue penetrability of NIR light compared with visible light. NIR light also effectively overcomes organism autofluorescence, making NIR QDs particularly attractive in biological imaging applications for disease diagnosis. Considering latest developments, Ag2 S QDs are a rising star among NIR QDs due to their excellent NIR fluorescence properties and biocompatibility. This review presents the various methods to synthesize NIR Ag2 S QDs, and systematically discusses their applications in biosensing, bioimaging, and theranostics. Major challenges and future perspectives concerning the synthesis and bioapplications of NIR Ag2 S QDs are discussed.

Excited-State Dynamics of Photoluminescent Gold Nanoclusters and Their Assemblies with Quantum Dot Donors

Gold nanoclusters (AuNCs) are a recently developed class of photoluminescent nanomaterial with potential for detection and imaging applications in both chemistry and biology. The AuNC small size (Au104NC) in combination with their long-lived, near-infrared (NIR) emission suggests that they could be applied as a biological label directly and also as a potential acceptor for energy transfer-based biosensing. Previous studies have shown that functionalized AuNCs can act as energy-transfer acceptors; however, the underlying mechanism appears to be complex and does not necessarily follow a classical Förster process with a (1/R)6 distance dependence. Here, we report a femtosecond and nanosecond time-resolved spectroscopy study to examine the energy dissipation and transfer processes of photoluminescent AuNC acceptors displaying different functionalized end groups and coupled with 625 nm emitting semiconductor quantum dot (QD) donors. Examination of AuNCs alone on the femtosecond timescale show coherent vibrational oscillations within the first 15 ps after excitation in the visible and NIR region. Fourier transform of the kinetic data reveal ∼0.18 and 0.40 THz low-frequency vibrations in aqueous AuNC solutions, with the latter attributed to coherent vibrations following hot electronic relaxation. A biphasic decay of the AuNC excited state on the microsecond timescales confirm their exceptionally long-lived lifetimes and that the photophysics is largely unaffected by the functional end group on the ligand. Finally, ultrafast studies of AuNCs coupled to the 625 QD donors reveal excited-state quenching and wavelength shifts of the QD’s ground-state bleach and the appearance of the excited state of the AuNC resulting from energy transfer occurring on the ∼200 ps timescale.

(Invited) Synthesis and Surface Engineering of III-V Semiconductor Quantum Dots for Infrared Optoelectronic Applications

Colloidal quantum dots (QDs) have widely been considered as emerging candidates for solution-processable optoelectronic devices. Especially, QDs that are optically active in NIR and SWIR spectral windows, offer a great promise for infrared emitters, infrared photodetectors, photovoltaics, and biological imaging applications. It is thus essential to develop high-quality infrared QDs without the use of heavy metals such as cadmium, lead, or mercury. Among various semiconducting materials, III-V compound semiconductors show great potential in practical optoelectronic applications not only due to their wide tunability in the infrared region, but also due to their excellent optical and electronic properties. However, the synthesis of III-V semiconductor-based QDs has been limited by the lack of understanding about the precursors of group V elements such as P, As and Sb. In this presentation, we would like to discuss about the pnictogen precursors to synthesize various III-V QDs and also the surface properties of the resultant QDs. By controlling the reaction process with the pnictogen precursors, we achieve size and stoichiometry-tunable III-V QDs including InP, InAs, InSb and alloy QDs. Based on structural, analytical, optical, and electrical characterization of the QDs, we study the effects of surface treatments on their optoelectronic properties. We demonstrate that III-V QD thin films are promising candidate materials for infrared optoelectronic devices. Figure 1

Preconditioned deconvolution method for high-resolution ghost imaging

Ghost imaging (GI) can nonlocally image objects by exploiting the fluctuation characteristics of light fields, where the spatial resolution is determined by the normalized second-order correlation function g ( 2 ) . However, the spatial shift-invariant property of g ( 2 ) is distorted when the number of samples is limited, which hinders the deconvolution methods from improving the spatial resolution of GI. In this paper, based on prior imaging systems, we propose a preconditioned deconvolution method to improve the imaging resolution of GI by refining the mutual coherence of a sampling matrix in GI. Our theoretical analysis shows that the preconditioned deconvolution method actually extends the deconvolution technique to GI and regresses into the classical deconvolution technique for the conventional imaging system. The imaging resolution of GI after preconditioning is restricted to the detection noise. Both simulation and experimental results show that the spatial resolution of the reconstructed image is obviously enhanced by using the preconditioned deconvolution method. In the experiment, 1.4-fold resolution enhancement over Rayleigh criterion is achieved via the preconditioned deconvolution. Our results extend the deconvolution technique that is only applicable to spatial shift-invariant imaging systems to all linear imaging systems, and will promote their applications in biological imaging and remote sensing for high-resolution imaging demands.

Cationic Tricyclic AIEgens for Concomitant Bacterial Discrimination and Inhibition.

New ionic compounds with aggregation-induced emission (AIE) feature has been widely studied. These AIE-based luminogens (AIEgens) not only effectively resolve aggregation-caused quenching (ACQ) problems that are encountered for most of conventional fluorescent dyes, but also exhibit promising applications in biological imaging, potentially for a wide variety of diseases. However, such an AIE system needs to be further developed. In this work, a series of novel cationic AIEgens that are comprised of tricyclic 2-aminopyridinium derivatives with seven-membered rings are designed and synthesized via a simple, multicomponent reaction. Notably, these AIEgens exhibit the ability to specifically stain gram-positive bacteria. Moreover, a specific AIEgen, BMTAP-7, possesses highly efficient bacteriostatic ability for Staphylococcus aureus (S. aureus) in both liquid medium and solid agar plates, which have a minimum inhibitory concentration (MIC) between 4 and 8 µg mL-1 . Using live-cell imaging and a wash-free process, it is observed that hydrophilic AIEgens are localized to mitochondria, whereas lipophilic AIEgens display specific staining of lysosomes. These AIEgens with bacteriostatic activity hold great promise for distinguishing between bacterial types and inhibiting bacterial infections in situ.

Optically Modulated and Optically Activated Delayed Fluorescent Proteins through Dark State Engineering.

Modulating fluorescent protein emission holds great potential for increasing readout sensitivity for applications in biological imaging and detection. Here, we identify and engineer optically modulated yellow fluorescent proteins (EYFP, originally 10C, but renamed EYFP later, and mVenus) to yield new emitters with distinct modulation profiles and unique, optically gated, delayed fluorescence. The parent YFPs are individually modulatable through secondary illumination, depopulating a long-lived dark state to dynamically increase fluorescence. A single point mutation introduced near the chromophore in each of these YFPs provides access to a second, even longer-lived modulatable dark state, while a different double mutant renders EYFP unmodulatable. The naturally occurring dark state in the parent YFPs yields strong fluorescence modulation upon long-wavelength-induced dark state depopulation, allowing selective detection at the frequency at which the long wavelength secondary laser is intensity modulated. Distinct from photoswitches, however, this near IR secondary coexcitation repumps the emissive S1 level from the long-lived triplet state, resulting in optically activated delayed fluorescence (OADF). This OADF results from secondary laser-induced, reverse intersystem crossing (RISC), producing additional nanosecond-lived, visible fluorescence that is delayed by many microseconds after the primary excitation has turned off. Mutation of the parent chromophore environment opens an additional modulation pathway that avoids the OADF-producing triplet state, resulting in a second, much longer-lived, modulatable dark state. These Optically Modulated and Optically Activated Delayed Fluorescent Proteins (OMFPs and OADFPs) are thus excellent for background- and reference-free, high sensitivity cellular imaging, but time-gated OADF offers a second modality for true background-free detection. Our combined structural and spectroscopic data not only gives additional mechanistic details for designing optically modulated fluorescent proteins but also provides the opportunity to distinguish similarly emitting OMFPs through OADF and through their unique modulation spectra.

Improvement of Gold Nanorods in Photothermal Therapy: Recent Progress and Perspective.

Cancer is a life-threatening disease, and there is a significant need for novel technologies to treat cancer with an effective outcome and low toxicity. Photothermal therapy (PTT) is a noninvasive therapeutic tool that transports nanomaterials into tumors, absorbing light energy and converting it into heat, thus killing tumor cells. Gold nanorods (GNRs) have attracted widespread attention in recent years due to their unique optical and electronic properties and potential applications in biological imaging, molecular detection, and drug delivery, especially in the PTT of cancer and other diseases. This review summarizes the recent progress in the synthesis methods and surface functionalization of GNRs for PTT. The current major synthetic methods of GNRs and recently improved measures to reduce toxicity, increase yield, and control particle size and shape are first introduced, followed by various surface functionalization approaches to construct a controlled drug release system, increase cell uptake, and improve pharmacokinetics and tumor-targeting effect, thus enhancing the photothermal effect of killing the tumor. Finally, a brief outlook for the future development of GNRs modification and functionalization in PTT is proposed.

Effect of Shape on the Entering of Graphene Quantum Dots into a Membrane: A Molecular Dynamics Simulation.

Graphene quantum dots (GQDs), a new quasi-zero-dimensional nanomaterial, have the advantages of a smaller transverse size, better biocompatibility, and lower toxicity. They have potential applications in biosensors, drug delivery, and biological imaging. Therefore, it is particularly important to understand the transport mechanism of the GQDs on the cell membrane. In particular, the effect of the GQD shapes on the translocation mechanism should be well understood. In this study, the permeation process of the GQDs with different shapes through a 1-palmitoyl-2-oleoylphosphatidylcholine membrane was studied using molecular dynamics. The results show that all small-sized GQDs with different shapes translocated through the lipid membrane at a nanosecond timescale. The GQDs tend to remain on the surface of the cell membrane; then, the corners of the GQDs spontaneously enter the cell membrane; and, finally, the entire GQDs enter the cell membrane and tend to stabilize in the middle of the cell membrane. Moreover, the GQDs do not induce notable damage to the cell membrane, indicating that they are less toxic to cells and can be used as a potential biomedical material.

Programmable Supercontinuum Laser Spectrum Generator Based on a Liquid-Crystal on Silicon Spatial Light Modulator

Supercontinuum (SC) lasers combine a broadband light spectrum with the unique properties of single-mode lasers. In this work we present an optical system to spectrally filter a SC laser source using liquid-crystal on silicon (LCoS) spatial light modulators (SLM). The proposed optical system disperses the input laser and the spectrally separated components are projected onto the LCoS-SLM, where the state of polarization of each wavelength is separately modulated. Finally, recombining the modulated spectral components results in an output laser source where the spectrum can be controlled dynamically from a computer. The system incorporates two branches to independently control the visible (VIS) and the near infrared (NIR) spectral content, thus providing a SC laser source from 450 to 1,600 nm with programmable spectrum. This new ability for controlling at will the wide spectra of the SC laser sources can be extremely useful for biological imaging applications.

Stimulated emission depletion microscopy for biological imaging in four dimensions: A review.

Stimulated emission depletion (STED) microscopy allows high lateral and axial resolution, long term imaging in living cells. Here we review recent technical advances in STED microscopy, with emphasis on resolution and measurement range of XYZt four dimensions. Different STED technical advances and novel STED probes are discussed with their respective application in biological subcellular imaging. This review may serve as a practical guide for choosing a suitable approach to the advanced STED super-resolution imaging.

Synthesis of water-soluble europium-containing nanoprobes via polymerization-induced self-assembly and their cellular imaging applications

Lanthanide nanoprobes have attracted extensive attention for applications in cellular imaging and biological sensing. Herein, water-dispersible europium (III)-based (Eu(III)-based) nanoprobes were prepared by reversible addition-fragmentation chain transfer (RAFT) polymerization-induced self-assembly (PISA) of hydrophobic monomers (Eu(III)-containing monomer and methyl methacrylate (MMA)) using hydrophilic macro-chain transfer agent poly(PEGMA)-CTA. The resulted poly(PMEu) nanoprobes showed spherical in shape in good monodispersity with average diameters of around 210 nm. The poly(PMEu) nanoprobles excellent aqueous dispersity, high aqueous stability and good luminescence properties with quantum yields of 37.21% and fluorescence lifetime of 312.4 μs. Moreover, the poly(PMEu) nanoprobes exhibited good cellular biocompatibility with cell viabilities of 88.2% and high fluorescence intensity for in vitro cellular imaging. The present approach provides a facile strategy for fabrication of luminescent Eu(III)-based nanoprobes with great potential applications for biological imaging.

Efficient External Energy Transfer from Mn-Doped Perovskite Nanocrystals.

Doping with a transition metal is an effective way to tune the optical properties of semiconductor nanocrystals (NCs). The excitation of transition-metal dopants in NCs is through an internal energy transfer from a host exciton, by which the short-lived exciton energy can be "stored" at the dopant for a significantly longer lifetime. Herein, using Mn-doped CsPbCl3 perovskite NCs as an example, we report that the long-lived excited state at Mn dopants can be efficiently extracted from the NCs through an external energy transfer (EET) to rhodamine B (RhB) molecules adsorbed on the NC surface. The EET process leads to a delayed RhB emission. The EET rate is found to increase from 0.16 to 1.42 ms-1 as the number of RhB molecules adsorbed per NC increases from 1 to 8.9, leading to energy extraction efficiency up to 71%. This work suggests the potential of Mn-doped perovskite NCs for applications in photon energy conversion and biological imaging.

Individual Plasmonic Nanoprobes for Biosensing and Bioimaging: Recent Advances and Perspectives.

With the advent of nanofabrication techniques, plasmonic nanoparticles (PNPs) have been widely applied in various research fields ranging from photocatalysis to chemical and bio-sensing. PNPs efficiently convert chemical or physical stimuli in their local environment into optical signals. PNPs also have excellent properties, including good biocompatibility, large surfaces for the attachment of biomolecules, tunable optical properties, strong and stable scattering light, and good conductivity. Thus, single optical biosensors with plasmonic properties enable a broad range of uses of optical imaging techniques in biological sensing and imaging with high spatial and temporal resolution. This work provides a comprehensive overview on the optical properties of single PNPs, the description of five types of commonly used optical imaging techniques, including surface plasmon resonance (SPR) microscopy, surface-enhanced Raman scattering (SERS) technique, differential interference contrast (DIC) microscopy, total internal reflection scattering (TIRS) microscopy, and dark-field microscopy (DFM) technique, with an emphasis on their single plasmonic nanoprobes and mechanisms for applications in biological imaging and sensing, as well as the challenges and future trends of these fields.

Fluorescent Pyrazole Derivatives: An Attractive Scaffold for Biological Imaging Applications

Among the huge number of fluorescent compounds described recently, pyrazole derivatives could play a paramount role in the design of probes for bioimaging applications–an important and simple tool for modern biology because of their easy synthetic methodologies, remarkable optical properties and chelating points. In this mini-review, we highlighted some pyrazole derivatives that have shown remarkable performance in this area; from the detection of chromium (III) with limits of detection of 37 × 10<sub>-12</sub> M to sensing glutathione in biological samples, as well as small molecule labeling of drugs and identifying unhealthy cells such as HeLa and labeling subcellular organelles. Evidently, this important class of N-heterocyclic compounds is part of interesting applications.

Fluorescent Determination of Butyrylcholinesterase Activity and Its Application in Biological Imaging and Pesticide Residue Detection.

Butyrylcholinesterase (BChE) is an essential human cholinesterase relevant to liver conditions and neurodegenerative diseases, which makes it a pivotal biomarker of health. It therefore remains challenging and highly desired to elaborate efficient chemical tools for BChE with simple operations and satisfactory working performance. In this work, a background-free detection strategy was built by virtue of the judicious coupling of a specific BChE-enzymatic reaction and in situ cyclization. High sensitivity with a low limit of detection (LOD) of 0.075 μg/mL could be readily achieved from the blank background and the as-produced emissive indicators, and the specific reaction site contributed to the high selectivity over other bio-species even acetylcholinesterase (AChE). In addition to the multifaceted spectral experiments to verify the sensing mechanism, this work assumed comprehensive studies on the application. The bio-investigation ranged from cells to an organism, declaring a noteworthy prospect in disease diagnosis, especially for Alzheimer's disease (AD), a common neurodegenerative disease with over-expressed BChE. Moreover, its excellent work for inhibition efficacy elucidation was also proved with the accuracy IC50 of tacrine for BChE (8.6 nM), giving rise to an expanded application for trace pesticide determination.

UWB-Printed Rectangular-Based Monopole Antenna for Biological Tissue Analysis

This paper presents the design of a printed step-type monopole antenna for biological tissue analysis and medical imaging applications in the microwave frequency range. The design starts from a very simple and widely known rectangular monopole antenna, and different modifications to the antenna geometry are made in order to increase the bandwidth. The antenna dimensions are optimized by means of a parametric analysis of each dimension using a 3-D electromagnetic simulator based on the finite element method. The optimized antenna, with final dimensions of 40 × 36 mm2, is manufactured onto a low-cost FR4 (fiber glass epoxy) substrate. The characteristics of the antenna have been measured inside an anechoic chamber, obtaining an omnidirectional radiation pattern and a working frequency range between 2.7 GHz and 11.4 GHz, which covers the UWB frequencies and enables the use of the antenna in medical imaging applications. Finally, the behaviour of four of these antennas located around a realistic breast model, made with biocompatible materials, has been analysed with the electromagnetic simulator, obtaining good results and demonstrating the usefulness of the designed antenna in the proposed application.