Biological Imaging Applications Research Articles

Metamaterial Lensing Devices

In recent years, the development of metamaterials and metasurfaces has drawn great attention, enabling many important practical applications. Focusing and lensing components are of extreme importance because of their significant potential practical applications in biological imaging, display, and nanolithography fabrication. Metafocusing devices using ultrathin structures (also known as metasurfaces) with superlensing performance are key building blocks for developing integrated optical components with ultrasmall dimensions. In this article, we review the metamaterial superlensing devices working in transmission mode from the perfect lens to two-dimensional metasurfaces and present their working principles. Then we summarize important practical applications of metasurfaces, such as plasmonic lithography, holography, and imaging. Different typical designs and their focusing performance are also discussed in detail.

Enzyme‐conjugated nanosensors with tunable detection limits for small biomolecule determination

AbstractPolymeric nanosensors are more appealing than electrochemical sensors for advanced biological imaging applications, but more development is required before polymeric nanosensors can achieve widespread application. The detection of small biomolecules without a suitable ionophore, such as the detection of glucose, depends on enzymatic recognition by mixing oxidase enzymes with nanosensors. However, conjugation schemes and response control methods are needed to make polymeric nanosensors suitable for real‐world applications. In this work, we develop enzyme‐conjugated nanosensors based on the biotin/avidin interaction with two unique structures. The response of the first structure is controllable through changes to the concentrations of enzyme and avidin as well as surface biotinylation level during synthesis, while the second structure requires a simpler synthesis and has a controllable response through changes to the surface biotinylation level. We also report findings about optimal avidin concentration and separation of unbound enzyme from the enzyme‐nanosensor conjugates through a magnetic purification approach.

A novel fluorescent chemosensor for detection of Zn(II) ions based on dansyl-appended dipeptide in two different living cells.

This paper describes a new fluorescent chemosensor (DSH) based on dipeptide conjugated with dansyl group, which was synthesized by solid phase peptide synthesis (SPPS) technology. DSH exhibited a highly selective and sensitive toward Zn2+ ions by "turn-on" response based on generation of monomer-excimer mechanism in aqueous solutions, and the detection limit was calculated at 11.2 nM. In addition, the reversible of DSH-Zn with Na2EDTA establishes the reuse of DSH, and the circulation effect was very good. Moreover, DSH had good water solubility, and was successfully applied to bioimage intracellular Zn2+ ions and Na2EDTA in two different living cells with exciting cellular permeability and low cytotoxicity, which indicated that DSH had great potential in the application of biological imaging.

Design and synthesis of nitrogen-fused pyridazinone fluorescent probes and their application in biological imaging

Design and synthesis of nitrogen-fused pyridazinone fluorescent probes and their application in biological imaging

Computational time-of-flight diffuse optical tomography

Imaging through a strongly diffusive medium remains an outstanding challenge in particular in association with applications in biological and medical imaging. Here we propose a method based on a single-photon time-of-flight camera that allows, in combination with computational processing of the spatial and full temporal photon distribution data, to image an object embedded inside a strongly diffusive medium over more than 80 transport mean free paths. The technique is contactless and requires one second acquisition times thus allowing Hz frame rate imaging. The imaging depth corresponds to several cm of human tissue and allows one to perform deep-body imaging, here demonstrated as a proof-of-principle.

Optics based biomedical imaging: Principles and applications

Biomedical optical imaging is an important subdivision of optical imaging with the aim of understanding the anatomy and function of life. In principle, biomedical optical imaging systems form an image by manipulating the excitation light and detecting the signals originating from light and tissue interactions. Ever since the invention of the first optical microscope over 1000 years ago, biomedical optical imaging technologies have been steadily evolving to enable faster, deeper, and higher resolution imaging. These technologies have led to a more comprehensive understanding of life at the macro-, micro-, and nanoscales and have improved clinical diagnosis and treatment. This tutorial provides an overview of biomedical optical imaging techniques and their applications. Based on the imaging depth, this tutorial classifies the current optical imaging systems into two regimes: diffraction and diffusion. Within each regime, a few commonly used imaging techniques and their biological imaging applications are discussed. Finally, we provide an outlook of future biomedical optical imaging.

Plasma Treatment Conversion of Phenolic Compounds into Fluorescent Organic Nanoparticles for Cell Imaging.

Fluorescent organic nanoparticles (FONs) are promising alternatives for biological imaging applications owing to the increasing concerns over the potential toxicity and poor degradability of inorganic particles-based probes. However, synthesis of stable, small-sized FONs in aqueous media remains challenging. Inspired by the self-polymerization chemistry of phenolic compounds, we demonstrate ultrafast synthesis of FONs (phenolic compound-derived FONs, PhFONs) from a variety of molecular building blocks including dopamine, norepinephrine, pyrogallol, and gallic acid, simply by nonthermlplasma treatment at the aqueous interface. Specifically, using dopamine as the precursor, poly(dopamine) (PD)-FONs featuring a small size of 3 nm are obtained within 1 min. Compositional and structural characterizations confirm the polymeric architectures in PD-FONs. The PhFONs, with multicolor emissions, excellent biocompatibility, high stability, and size-dependent access into cell nucleus, are suitable for live cell imaging and developing nucleus-targeting imaging platforms.

Room‐Temperature Phosphorescence in Metal‐Free Organic Materials

AbstractPurely organic materials with room‐temperature phosphorescence (RTP) have attracted a growing interest for their potential applications in biological imaging, digital encryption, optoelectronic devices, and so on. To date, many strategies have succeeded in designing efficient organic RTP materials by overcoming the spin‐forbidden transition between singlet and triplet states. However, the underlying mechanisms of RTP still remain ambiguous. Such spin prohibition in phosphorescence are clarified, herein, from the perspective of perturbation theory, helping to understand the intrinsic relationship among various phosphorescence parameters, like phosphorescence efficiency, lifetime, intersystem crossing rate, as well as radiative and nonradiative rates. Taking into consideration the recent progress in organic RTP materials, these factors are further illustrated by a selection of the most relevant molecules. In addition, some novel RTP phenomena are also reviewed, thus providing an excellent guideline to constructing efficient RTP materials.

Li5 Zn8 Ga5 Ge9 O36 : Cr3+ , Ti4+ : A Long Persistent Phosphor Excited in a Wide Spectral Region from UV to Red Light for Reproducible Imaging through Biological Tissue.

Near-infrared (NIR) long-persistent phosphors (LPPs) have emerged as a potential solution for bio-imaging applications over the past few years. However, there are enormous challenges regarding their in situ application based on their dependence on short-wavelength excitation. In this paper, we report a multi-spectral excited NIR LPP, Li5 Zn8 Ga5 Ge9 O36 : 1.5 % Cr3+ , 0.5 % Ti4+ , which overcomes the limitations of functional processes in biological tissues and other complex systems. This LPP exhibits a high luminescent intensity and a long emission duration in the NIR region (700-800 nm). The applicability of this phosphor to tissue imaging is demonstrated experimentally. Its persistent luminescence (PersL) can easily penetrate approximately 2 mm of pork flesh. More importantly, this phosphor can be re-charged in situ using a red LED or laser diode array to provide renewed NIR PersL for biological tissues, which is beneficial for long-term biological tissue imaging applications with high signal-to-noise ratios. Systematic investigations of the nature of energy traps and PersL mechanisms are also reported in this paper.

Bifunctional Pyrrolidin-2-one Terminated Manganese Oxide Nanoparticles for Combined Magnetic Resonance and Fluorescence Imaging.

Multimodal probes are an asset for simplified, improved medical imaging. In particular, fluorescence and magnetic resonance imaging (MRI) are sought-after combined capabilities. Here, we show that pyrrolidin-2-one-capped manganese oxide nanoparticles (MnOpyrr NPs) combine MRI with fluorescence microscopy to function as efficient bifunctional bio-nanoprobes. We employ a one-pot synthesis for ca. 10 nm MnO NPs, wherein manganese(II) 2,4-pentadionate is thermally decomposed using pyrrolidin-2-one as a solvent and capping ligand. The MnOpyrr NPs are soluble in water without any further postsynthetic modifications. The r1 relaxivity and r2 /r1 ratio indicate that these NPs are potential T1 MRI contrast agents at clinical (3 T) and ultrahigh (9.4 T) magnetic fields. Serendipitously, the as-prepared NPs are photoluminescent. The unexpected luminescence is ascribed to the modification of the pyrrolidin-2-one during the thermal treatment. MnOpyrr NPs are successfully used to enable fluorescence microscopy of HeLa cells, demonstrating bifunctional imaging capabilities. A low cytotoxic response in two distinct cell types (HeLa, HepG2) supports the suitability of MnOpyrr NPs for biological imaging applications.

Poly(2-oxazoline)-based nanoparticles with aggregation-induced emission (AIE) for targeted cell imaging

Poly(2-oxazoline)-based nanoparticles with AIE feature were prepared for targeted cell imaging. First, P(EtOx-BuOx) was fabricated by subsequent cationic ring-opening polymerization (CROP). Then, the folate was attached to the end chains of P(EtOx-BuOx). AIE-active TPEMN was conjugated to the side chains of P(EtOx-BuOx) through ‘‘thio-ene’’ click reactions. Cellular experiments demonstrated that the nanocomposites had well dispersity in the physiological environment and could be internalized by folate receptor (FR)-positive cells. We envision that this research endows a simple approach to the fabrication of stable fluorescent polymeric nanocomposites, which display favorable biocompatibility and immense potential for applications in biological imaging and cell detection.

Temperature dependent optical and dielectric properties of liquid water studied by terahertz time-domain spectroscopy

Terahertz waves have found wide applications in the biological and medical areas. Since water is one of the most important ingredients in the biological systems, it is necessary to investigate its optical and dielectric properties in the terahertz range. These fundamental physical parameters play an important role in many applications, such as biological imaging and hyperthermia applications, and are temperature dependent. In order to shed more light on the property of temperature dependence, we performed a systematic investigation by changing the temperature of the water sample and using a terahertz time-domain spectrometer. The experimental results show that when the temperature increases from 275 K to 340 K, the refractive index and the complex dielectric constant of water increase noticeable, with the absorption coefficient increased observably. A good agreement is found between experimental data and the double Debye model.

In situ 3D reconfigurable ultrasonically sculpted optical beam paths.

We demonstrate that optical beams can be spatially and temporally shaped in situ by forming 3D reconfigurable interference patterns of ultrasound waves in the medium. In this technique, ultrasonic pressure waves induce a modulated refractive index pattern that shapes the optical beam as it propagates through the medium. Using custom-designed cylindrical ultrasonic arrays, we demonstrate that complex patterns of light can be sculpted in the medium, including dipole and quadrupole shapes. Additionally, through a combination of theory and experiment, we demonstrate that these optical patterns can be scanned in radial and azimuthal directions. Moreover, we show that light can be selectively confined to different extrema of the spatial ultrasound pressure profile by temporally synchronizing lightwave and ultrasound. Finally, we demonstrate that this technique can also be used to define spatial patterns of light in turbid media. The notion of in situ 3D sculpting of optical beam paths using ultrasound interference patterns can find intriguing applications in biological imaging and manipulation, holography, and microscopy.

Flexible Light-Sheet Generation by Field Synthesis

Light-sheet microscopy has revolutionized biological imaging by affording rapid and efficient volumetric imaging while minimizing the applied light-dosage and thus phototoxicity. However, due to beam divergence, there is a trade-off between the light-sheet thickness and the useful field-of-view for imaging: the confocal parameter, which approximates the propagation length of a light-sheet, shrinks nonlinearly with the size of the beam waist, and consequently, modest axial resolution is achieved when imaging large specimens. To overcome this trade-off, propagation invariant beams have been employed in light-sheet generation, such as Bessel or Airy beams. These beams maintain their cross-sectional profile over extended distances and overcome the beam divergence of Gaussian beams. To generate a light-sheet, a propagation invariant beam is scanned laterally to create a time averaged sheet of light. Such setups require dedicated optical trains, which increase the cost and complexity of a light-sheet microscope. We have recently discovered and proven the ‘Field Synthesis’ theorem, which describes a universal mechanism for light-sheet generation. Field synthesis predicts that any scanned light-sheet can be synthesized by an incoherent superposition of 1D intensity patterns. We demonstrate that in practice, this results in far less complex optical systems and much higher light-efficiency compared to previous setups using propagation invariant beams. Through careful comparisons, we show that through Field Synthesis we can re-create the time averaged intensity of Bessel and Lattice light-sheets. However, in contrast to scanned Bessel beams, we achieve 100% spatial duty cycle, which results in drastically reduced photobleaching. Compared to lattice light-sheet microscopy, Field Synthesis is achromatic and can hence perform simultaneous multicolor imaging. We present careful comparisons of each illumination mode and demonstrate biological imaging applications of light-sheets produced by Field Synthesis.

Synthesis and spectral analysis of fluorescent probes for Ce4+ and OCl- ions based on fluorescein Schiff base with amino or hydrazine structure: Application in actual water samples and biological imaging.

Two Schiff base fluorescein probes (FDA, FDH) based on fluorescein-aldehyde and nitroaniline derivatives were synthesized. The effects of amino and hydrazine substituents in fluorescein backbones were examined via fluorescence and absorbance spectra. In the presence of Ce4+, the fluorescence of FDA was quenched due to the ligand to metal charge transfer (LMCT). Hypochloric acid can react with the CN bond, and blocking the photo induced electron transfer (PET) of FDH leads to enhancement of the fluorescence. FDA showed detection limits for Ce4+ and OCl- as low as 63 nM in concentration range of 0-4 μM. FDH showed detection limits for OCl- as low as 0.8 μM in concentration rang 0-100 μM. Polyvinylidene fluoride (PVDF) membrane containing the probes was prepared for the real-time qualitative detection of Ce4+ and OCl- in real water samples. The probes were successfully applied to biological imaging in vascular smooth muscle cells (VSMCs) and are expected to find applications in biosensing.

Synthesis of fluorescent molybdenum nanoclusters at ambient temperature and their application in biological imaging

We introduce for first time a facile protocol for the rapid synthesis of a molybdenum nanoclusters (MoNCs) at room temperature using thiolated dithiothreitol (DTT) as capping agents. The initial fluorescence from the MoNCs is observed in 30 min and further intensified in 48 h. The mean diameter of nanoclusters was found to be 1.5 nm with −77 mV zeta potential. The nanoclusters have good stability in all tested pH ranges, especially between pH 7 and 10. This property makes the nanomaterial to be ideal for many types of possible biological/biomedicine applications such as drug delivery or biological imaging. The quantum yield of thiolated MoNCs was calculated to be 59% which is higher than the noble metal nanoclusters reported earlier. The mechanism of formation of MoNCs was investigated using the UV–Vis spectroscopy and cyclic voltammetry. Owing to these characteristics, MoNCs were used for imaging of HaCaT and A549 cancer cells. The current approach on novel synthesis of MoNCs is found to be a superior alternative to conventional/popular MoS2 based on the method of synthesis, particle size, and fluorescence quantum yield. The current approach on the MoNCs has created a new platform for future biomedicine applications.

Chemical Synthesis and Applications of Colloidal Metal Phosphide Nanocrystals.

Colloidal nanocrystals (NCs) have emerged as promising materials in optoelectronic devices and biological imaging application due to their tailorable properties through size, shape, and composition. Among these NCs, metal phosphide is an important class, in parallel with metal chalcogenide. In this review, we summarize the recent progress regarding the chemical synthesis and applications of colloidal metal phosphide NCs. As the most important metal phosphide NCs, indium phosphide (InP) NCs have been intensively investigated because of their low toxicity, wide and tunable emission range from visible to the near-infrared region. Firstly, we give a brief overview of synthetic strategies to InP NCs, highlighting the benefit of employing zinc precursors as reaction additive and the importance of different phosphorus precursors to improve the quality of the InP NCs, in terms of size distribution, quantum yield, colloidal stability, and non-blinking behavior. Next, we discuss additional synthetic techniques to overcome the issues of lattice mismatch in the synthesis of core/shell metal phosphide NCs, by constructing an intermediate layer between core/shell or designing a shell with gradient composition in a radial direction. We also envision future research directions of InP NCs. The chemical synthesis of other metal phosphide NCs, such as II–V metal phosphide NCs (Cd3P2, Zn3P2) and transition metal phosphides NCs (Cu3P, FeP) is subsequently introduced. We finally discuss the potential applications of colloidal metal phosphide NCs in photovoltaics, light-emitting diodes, and lithium ion battery. An overview of several key applications based on colloidal metal phosphide NCs is provided at the end.

Near-Infrared Light-Activated CuFeSe2 Hierarchical Nanostructures: Synthesis, Characterization, and Growth Mechanism

Near-infrared light-activated nanomaterials are of promising potential for phototherapies and biological imaging applications. Despite that well-developed syntheses are available for zero-dimensional CuFeSe2 nanoparticles, the synthesis of two-dimensional CuFeSe2 nanosheets remains a big challenge. Here, we report for the first time the preparation of CuFeSe2 hierarchical nanostructures assembled from nanosheets via a facile cation exchange method. A possible formation mechanism of CuFeSe2 hierarchical nanostructures has been proposed. By carefully optimizing reaction parameters, including growth and exchange times as well as the initial reactant ratios, high-quality CuFeSe2 hierarchical nanostructures are achieved, exhibiting an intense photoabsorption region from 400 to 1700 nm. This study sheds light on a new approach to design and develop the near-infrared light-activatable CuFeSe2 hierarchical nanostructures as multifunctional nanomaterials potential for the imaging-guided photothermal therapy of tumors.

Strategies for designing organic fluorescent probes for biological imaging of reactive carbonyl species.

Reactive carbonyl species (RCS) are involved not only in diverse physiological pathways but also in various pathological processes, including Alzheimer's disease, diabetes, cardiovascular disease, and other malignant diseases. Therefore, it is essential to develop a simple and sensitive technology which can be employed to selectively monitor RCS in living biological samples, such as living cells, tissues, and animals. The subtle changes in the concentration of RCS in organisms can be detected by this technique. In this review, the design strategies of the typical examples of RCS fluorescent probes are highlighted and discussed. These advanced RCS probes may set the foundation for biomedical research on dynamic real-time monitoring of RCS in living systems.

Water-soluble chiral CdSe/CdS dot/rod nanocrystals for two-photon fluorescence lifetime imaging and photodynamic therapy.

Compared with traditional organic contrast agents, semiconductor nanocrystals (NCs) have unique optical properties that are vital for biological applications with ultrahigh sensitivities, such as long fluorescence lifetime and large multiphoton absorption (MPA). However, the MPA properties and biological applications of chiral-ligand-stabilized semiconductor NCs have scarcely been reported, which seriously hinders their relevant applications. In this work, we report the aqueous phase transfer of CdSe/CdS dot/rod NCs with the use of cysteine molecules, after which the NCs preserve their high fluorescence quantum yield, long lifetime, and efficient circular dichroism. More importantly, the investigated dot/rod NCs show extremely large two- and three-photon absorption action cross-sections in the first and second biological windows, with maximum values of ∼21 000 GM at 800 nm and ∼4.6 × 10-78 cm6 s2 per photon2 at 1300 nm, which are among the largest values reported for water-soluble fluorescent nanoparticles. Interestingly, the dot/rod NCs exhibit a high singlet oxygen generation efficiency of 35%. In addition, for the first time, two-photon fluorescence lifetime imaging and photodynamic therapy of the dot/rod NCs were successfully demonstrated. The performed investigation of the optical properties of these water-soluble CdSe/CdS dot/rod NCs indicates that they are promising candidates for nonlinear biological imaging applications.