Nanoscale optical probes for cellular imaging

Recent Developments in SERS Microfluidic Chips: From Fundamentals to Biosensing Applications

This paper reviews the latest research progress of surface-enhanced Raman spectroscopy (SERS) microfluidic chips in the field of biosensing. Due to its single-molecule sensitivity, selectivity, minimal or no preprocessing, and immediacy, SERS is considered a promising biosensing technology. However, the nondirectional interactions between biological samples and the substrate, as well as fluctuations in the sample environment temperature during signal acquisition, can affect the stability and reproducibility of SERS signals. Integrating SERS spectroscopy with microfluidic chips not only leverages the continuous sample flow, high reaction efficiency, high throughput, and multifunctionality of microfluidic chips to address challenges in biosensing applications but also expands the scope of microfluidic technology by providing a novel on-chip optical detection method. The combination of SERS and microfluidic chips not only enables the complementary advantages of both technologies but also offers a highly promising "combined technology" for the field of biosensing. This paper starts by introducing the enhancement mechanisms of SERS and presents both labeled and label-free SERS strategies. Based on the differences in substrate properties, we broadly categorize SERS microfluidic chips into colloidal nanoparticle-based SERS microfluidic chips and fixed substrate-based SERS microfluidic chips. Finally, we review the latest research progress on SERS microfluidic chips for biosensing biological targets such as nucleic acids, proteins, small biomolecules, and live cells. In the conclusion and outlook section, we summarize the challenges faced by SERS microfluidic chips in biosensing and propose feasible solutions. To better leverage the role of SERS microfluidic chips in biosensing, we also present an outlook on the future development of this combined technology.

Bioparameter-directed nanoformulations as MRI CAs enable the specific visualization of hypoxic tumour

A malignant tumour has hypoxic cells of varying degrees. The more severe the hypoxic degree, the more difficult the prognosis of the tumour and the higher the recurrence rate. Therefore, tumour hypoxia imaging is crucial. Magnetic resonance imaging (MRI) shows its strength in high resolution, depth of penetration and noninvasiveness. However, it needs more excellent contrast agents (CAs) to combat the complex tumour microenvironment (TME) and increased targeting of tumours to enhance clinical safety. Many research studies have focused on developing hypoxia-responsive MRI CAs that take advantage of the unique characteristics of hypoxic tumours. The low oxygen pressure, acidic TME, and up-regulated redox molecule levels found in hypoxic tumours serve as biological stimuli for nanoformulations that can accurately image the hypoxic region. This review highlights the importance of developing bioparameter-directed nanoformulations as MRI CAs for accurate tumour diagnosis. The design strategies and mechanisms of tumour-hypoxia imaging with nanoformulations are exemplified, with a focus on pH-responsiveness, redox-responsiveness, and p(O2)-responsiveness. The promising future of bioparameter-responsive nanoformulations for accurate tumour diagnosis and personalised cancer treatment is discussed.

Persistent luminescent metal-organic framework nanocomposite enables autofluorescence-free dual modal imaging-guided drug delivery

Molecular imaging-guided therapy was essential for realizing precise cancer intervention, while designing an imaging platform to achieve autofluorescence-free imaging for dual modal imaging-guided drug delivery remains a challenge. Near-infrared persistent luminescence nanoparticles (NIR PLNPs) were promising for tumor imaging due to no background interference from the tissue. Herein, a persistent luminescent metal-organic framework (PLNPs@MIL-100(Fe)) is prepared via a layer-by-layer method for dual-modal imaging-guided drug delivery. The PLNPs@MIL-100(Fe) exhibit NIR persistent luminescence emitting and T₂-weighted signal, achieving precise in vivo dual-modal imaging of tumor-bearing mice by providing high spatial resolution MR imaging and autofluorescence-free NIR imaging. The porous MIL-100(Fe) shell provides PLNPs@MIL-100(Fe) with up to 87.1% drug loading capacity and acid-triggered drug release for drug delivery. We envision that the proposed PLNPs@MIL-100(Fe) platform would provide an effective approach for precise tumor imaging and versatile drug delivery.

Biomimetic lipid-fluorescein probe for cellular bioimaging

Fluorescence probe is one of the most powerful tools for cellular imaging. Here, three phospholipid-mimicking fluorescent probes (FP1-FP3) comprising fluorescein and two lipophilic groups of saturated and/or unsaturated C18 fatty acids were synthesized, and their optical properties were investigated. Like in biological phospholipids, the fluorescein group acts as a hydrophilic polar headgroup and the lipid groups act as hydrophobic non-polar tail groups. Laser confocal microscope images illustrated that FP3, which contains both saturated and unsaturated lipid tails, showed great uptake into the canine adipose-derived mesenchymal stem cells.

Development of a NIR iridium(III) complex for self-calibrated and luminogenic detection of boron trifluoride

Boron trifluoride (BF3) is a potential environmental pollutant, and excess exposure to it may cause human diseases. However, the sensitive, rapid and accurate detection of BF3 for on-site purposes is still a challenge. In this work, we developed the first NIR iridium(III)-based probe with dual emission and a Stokes shift of 370 nm for self-calibrated and luminogenic detection of BF3. This probe exhibited a strong luminescence enhancement at around 650 nm to BF3 (0-100 μM) with almost no change in luminescence at 475 nm, displaying a 220-fold I650 nm/I475 nm enhancement at 100 μM of BF3 with a detection limit of 0.35 μM. Moreover, the probe showed a fast response time of less than 5 s to BF3 along with an obvious color change under UV irradiation for visual detection. Importantly, the desirable photophysical properties of the iridium(III)-based probe can be harnessed for time-resolved detection of BF3 in the presence of the fluorescence background. The applicability of the probe was further verified in an organic solvent waste-spiked system and on a glass pane. This work will provide a solid basis for the development of sensitive and on-site BF3 sensing toolkits for environmental monitoring.

Uncovering the Interaction between Intracellular Telomerase Activity and Hydrogen Peroxide during Cancer Cell Apoptosis Utilizing a Dual-Color Fluorescent Nanoprobe

Uncovering the intrinsic interaction of different bioactive species, i.e., reactive oxygen species (ROS) and telomerase, is of great importance because they play interrelated and interdependent biological roles in living organisms. Nevertheless, exploration of the intracellular ROS/telomerase cross-talk by effective and noninvasive methods remains a great challenge, as it is difficult to simultaneously detect different types of biomolecules (i.e., active small molecules and proteins) in living cells. To address this issue, herein, we report, for the first time, a novel fluorescent nanoprobe for simultaneous determination and in situ imaging of telomerase activity and hydrogen peroxide (H₂O₂) in living cells. With the advantage of high sensitivity and good specificity, this newly fabricated nanoprobe was successfully applied to precisely visualize and monitor the changes in telomerase activity and H₂O₂ concentration in cancer cells. More significantly, by employing the nanoprobe as a one-step incubation tool, it is found that there is a cross-talk between H₂O₂ and telomerase activity in the drug-induced cancer cells' apoptosis process, which provides valuable information for gaining fundamental insights into the relationship between ROS and telomerase activity in cancer treatments. This work affords a promising method for revealing the relevant regulatory mechanisms and roles of ROS and telomerase activity in the occurrence, evolvement, and treatment of diseases.

Dual-wavelength photoacoustic atlas method to estimate fractional methylene blue and hemoglobin contents

SIGNIFICANCE

Methylene blue (MB) is an exogenous contrast agent that has the potential to assist with visualization and penetration challenges in photoacoustic imaging. However, monitoring the local concentration between MB and endogenous chromophores is critical for avoiding unnecessary MB accumulations that could lead to adverse effects such as hemolysis when exposed to increased dose and photodamage when exposed to high laser energies.

AIM

We developed a modified version of a previously proposed acoustic-based atlas method to estimate concentration levels from a mixture of two photoacoustic-sensitive materials after two laser wavelength emissions.

APPROACH

Photoacoustic data were acquired from mixtures of 100-μM MB and either human or porcine blood (Hb) injected in a plastisol phantom, using laser wavelengths of 710 and 870 nm. An algorithm to perform linear regression of the acoustic frequency response from an atlas composed of pure concentrations was designed to assess the concentration levels from photoacoustic samples obtained from 11 known MB/Hb volume mixtures. The mean absolute error (MAE), coefficient of determination (i.e., R2), and Spearman's correlation coefficient (i.e., ρ) between the estimated results and ground-truth labels were calculated to assess the algorithm performance, linearity, and monotonicity, respectively.

RESULTS

The overall MAE, R2, and ρ were 12.68%, 0.80, and 0.89, respectively, for the human Hb dataset and 9.92%, 0.86, and 0.93, respectively, for the porcine Hb dataset. In addition, a similarly linear relationship was observed between the acoustic frequency response at 2.3 MHz and 870-nm laser wavelength and the ground-truth concentrations, with R2 and | ρ | values of 0.76 and 0.88, respectively.

CONCLUSIONS

Contrast agent concentration monitoring is feasible with the proposed approach. The potential for minimal data acquisition times with only two wavelength emissions is advantageous toward real-time implementation in the operating room.

Facets of optically and magnetically induced heating in ferromagnetically doped-NaYF4 particles

Upconverting particles like Yb and Er-doped NaYF₄ are known to heat up after illumination with light at pump wavelength due to inefficient upconversion processes. Here we show that NaYF₄ particles which have been co-doped not only with Yb and Er but also Fe improves the photothermal conversion efficiency. In addition, we show for the first time that alternating magnetic fields also heat up the ferromagnetic particles. Thereafter we show that a combination of optical and magnetic stimuli significantly increases the heat generated by the particles.

The In Vivo Toxicity Assessments of Water-Dispersed Fluorescent Silicon Nanoparticles in Caenorhabditis elegans

Fluorescent silicon nanoparticles (SiNPs), resembling a typical zero-dimensional silicon nanomaterial, have shown great potential in a wide range of biological and biomedical applications. However, information regarding the toxicity of this material in live organisms is still very scarce. In this study, we utilized Caenorhabditis elegans (C. elegans), a simple but biologically and anatomically well-described model, as a platform to systematically investigate the in vivo toxicity of SiNPs in live organisms at the whole-animal, cellular, subcellular, and molecular levels. We calculated the effect of SiNPs on C. elegans body length (N ≥ 75), lifespan (N ≥ 30), reproductive capacity (N ≥ 10), endocytic sorting (N ≥ 20), endoplasmic reticulum (ER) stress (N ≥ 20), mitochondrial stress (N ≥ 20), oxidative stress (N ≥ 20), immune response (N ≥ 20), apoptosis (N ≥ 200), hypoxia response (N ≥ 200), metal detoxification (N ≥ 200), and aging (N ≥ 200). The studies showed that SiNPs had no significant effect on development, lifespan, or reproductive ability (p > 0.05), even when the worms were treated with a high concentration (e.g., 50 mg/mL) of SiNPs at all growth and development stages. Subcellular analysis of the SiNP-treated worms revealed that the intracellular processes of the C. elegans intestine were not disturbed by the presence of SiNPs (p > 0.05). Toxicity analyses at the molecular level also demonstrated that the SiNPs did not induce harmful or defensive cellular events, such as ER stress, mitochondria stress, or oxidative stress (p > 0.05). Together, these findings confirmed that the SiNPs are low in toxicity and biocompatible, supporting the suggestion that the material is an ideal fluorescent nanoprobe for wide-ranging biological and biomedical applications.

Reaction-based fluorescent and chemiluminescent probes for formaldehyde detection and imaging

Formaldehyde (FA), a reactive carbonyl species, is classified as Group 1 carcinogen by International Agency for Research on Cancer (IARC) in 2004. In addition, clinical studies have implicated that elevated levels of FA have been associated with different kinds of diseases, such as neurodegenerative diseases, diabetes, and chronic liver and heart disorders. However, in addition to the direct inhalation of FA in the environment, most organisms can also produce FA endogenously by demethylases and oxidases during the metabolism of amino acids and xenobiotics. Since FA plays an important role in physiological and pathological processes, developing reliable and efficient methods to monitor FA levels in biological samples is crucial. Reaction-based fluorescent/chemiluminescent probes have provided robust methods for FA detection and real-time visualization in living organisms. In this highlight, we will summarize the major developments in the structure design and applications of FA probes in recent years. Three main strategies for designing FA probes have been discussed and grouped by different reaction mechanisms. In addition, some miscellaneous reaction mechanisms have also been discussed. We also highlight novel applications of these probes in biological systems, which offer powerful tools to discover the diverse functions of FA in physiology and pathology processes.

Interfacially Super-Assembled Benzimidazole Derivative-Based Mesoporous Silica Nanoprobe for Sensitive Copper (II) Detection and Biosensing in Living Cells

Mesoporous silica nanoparticles (MSNs) functionalized with benzimidazole-derived fluorescent molecules (DHBM) are fabricated via a feasible interfacial superassembly strategy for the highly sensitive and selective detection of Cu²⁺ . DHBM-MSN exhibits an obvious quenching effect on Cu²⁺ in aqueous solutions, and the detection limit can be as low as 7.69×10^-8  M. The DHBM-MSN solid-state sensor has good recyclability, and the silica framework can simultaneously improve the photostability of DHBM. Two mesoporous silica nanoparticles with different morphologies were specially designed to verify that nanocarriers with different morphologies do not affect the specific detectionability. The detection mechanism of the fluorescent probe was systematically elucidated by combining experimental results and density function theory calculations. Moreover, the detection system was successfully applied to detect Cu²⁺ in bovine serum, juice, and live cells. These results indicate that the DHBM-MSN fluorescent sensor holds great potential in practical and biomedical applications.

Smart Cargo Delivery System based on Mesoporous Nanoparticles for Bone Disease Diagnosis and Treatment

Bone diseases constitute a major issue for modern societies as a consequence of progressive aging. Advantages such as open mesoporous channel, high specific surface area, ease of surface modification, and multifunctional integration are the driving forces for the application of mesoporous nanoparticles (MNs) in bone disease diagnosis and treatment. To achieve better therapeutic effects, it is necessary to understand the properties of MNs and cargo delivery mechanisms, which are the foundation and key in the design of MNs. The main types and characteristics of MNs for bone regeneration, such as mesoporous silica (mSiO2 ), mesoporous hydroxyapatite (mHAP), mesoporous calcium phosphates (mCaPs) are introduced. Additionally, the relationship between the cargo release mechanisms and bone regeneration of MNs-based nanocarriers is elucidated in detail. Particularly, MNs-based smart cargo transport strategies such as sustained cargo release, stimuli-responsive (e.g., pH, photo, ultrasound, and multi-stimuli) controllable delivery, and specific bone-targeted therapy for bone disease diagnosis and treatment are analyzed and discussed in depth. Lastly, the conclusions and outlook about the design and development of MNs-based cargo delivery systems in diagnosis and treatment for bone tissue engineering are provided to inspire new ideas and attract researchers' attention from multidisciplinary areas spanning chemistry, materials science, and biomedicine.

Green light-emitting BSA-conjugated dye supported silica nanoparticles for bio-imaging applications

BSA conjugated with amine functionalised silica nanoparticles (BSA@DSFN) proved to be an ideal material for long life fluorescent probe for cellular imaging application.

Nano versus Molecular: Optical Imaging Approaches to Detect and Monitor Tumor Hypoxia

Hypoxia is a ubiquitous feature of solid tumors, which plays a key role in tumor angiogenesis and resistance development. Conventional hypoxia detection methods lack continuous functional detection and are generally less suitable for dynamic hypoxia measurement. Optical sensors hereby provide a unique opportunity to noninvasively image hypoxia with high spatiotemporal resolution and enable real-time detection. Therefore, these approaches can provide a valuable tool for personalized treatment planning against this hallmark of aggressive cancers. Many small optical molecular probes can enable analyte triggered response and their photophysical properties can also be fine-tuned through structural modification. On the other hand, optical nanoprobes can acquire unique intrinsic optical properties through nanoconfinement as well as enable simultaneous multimodal imaging and drug delivery. Furthermore, nanoprobes provide biological advantages such as improving bioavailability and systemic delivery of the sensor to enhance bioavailability. This review provides a comprehensive overview of the physical, chemical, and biological analytes for cancer hypoxia detection and focuses on discussing the latest nano- and molecular developments in various optical imaging approaches (fluorescence, phosphorescence, and photoacoustic) in vivo. Finally, this review concludes with a perspective toward the potentials of these optical imaging approaches in hypoxia detection and the challenges with molecular and nanotechnology design strategies.

New technologies in breast cancer sentinel lymph node biopsy; from the current gold standard to artificial intelligence

Sentinel lymph node biopsy is an important diagnostic procedure performed in early breast cancer patients with clinically negative axillary lymph nodes. Detection and examination of sentinel lymph nodes determine further therapy decisions, therefore a choice of optimal technique minimising the risk of false-negative results is of great importance. Currently, the gold standard is the dual technique comprising the blue dye and radiotracer, however, this method creates a logistical problem for many medical units. The intrinsic constraints of the existing methods led to the development of a very wide range of alternatives with varying clinical efficiency and feasibility. While each method presents with its own advantages and disadvantages, many techniques have improved enough to become a non-inferior alternative in the sentinel lymph node biopsy. Along with the improvement of the existing technologies, there are evolving trends such as multimodality of the techniques maximising the diagnostic outcome or an emerging use of artificial intelligence (AI) improving the workflow of the procedure. This literature review aims to give an overview of the current status of the standard techniques and emerging cutting-edge technologies in the sentinel lymph node biopsy.

Impact of the Interband Transitions in Gold and Silver on the Dynamics of Propagating and Localized Surface Plasmons

Understanding and modeling of a surface-plasmon phenomenon on lossy metals interfaces based on simplified models of dielectric function lead to problems when confronted with reality. For a realistic description of lossy metals, such as gold and silver, in the optical range of the electromagnetic spectrum and in the adjacent spectral ranges it is necessary to account not only for ohmic losses but also for the radiative losses resulting from the frequency-dependent interband transitions. We give a detailed analysis of Surface Plasmon Polaritons (SPPs) and Localized Surface Plasmons (LPSs) supported by such realistic metal/dielectric interfaces based on the dispersion relations both for flat and spherical gold and silver interfaces in the extended frequency and nanoparticle size ranges. The study reveals the region of anomalous dispersion for a silver flat interface in the near UV spectral range and high-quality factors for larger nanoparticles. We show that the frequency-dependent interband transition accounted in the dielectric function in a way allowing reproducing well the experimentally measured indexes of refraction does exert the pronounced impact not only on the properties of SPP and LSP for gold interfaces but also, with the weaker but not negligible impact, on the corresponding silver interfaces in the optical ranges and the adjacent spectral ranges.

Direct carbonization of organic solvents toward graphene quantum dots

The bottom-up synthesis of graphene quantum dots (GQDs) using solvothermal methods has attracted considerable attention because of their fewer defects and controllable size/morphology. However, the influence of organic solvents on the preparation of GQDs is still unknown. Herein, a systematic study on the carbonization of organic solvents toward GQDs is reported. The results show that organic solvents with the double bond or benzene ring or double hydrophilic groups could be directly decomposed into GQDs without the addition of catalysts or molecular precursors. The as-synthesized GQDs demonstrate ultra-small size distribution, high stability, tunable excitation wavelength and upconverted fluorescence. Both hematological and histopathological analyses show that the as-synthesized GQDs demonstrate a very good safety profile and excellent biocompatibility. The versatility of this synthesis strategy offers easy control of the surface group, composition, and optical properties of GQDs at the molecular level.

Fluorescent, colourimetric, and ratiometric probes based on diverse fluorophore motifs for mercuric(II) ion (Hg2+) sensing: highlights from 2011 to 2019

Though it has not been shown to deliver any biological importance, mercuric(II) ion (Hg²⁺) is a deleterious cation which poses grievous effects to the human body and/or the ecosystem, hence, the need for its sensitive and selective monitoring in both environmental and biological systems. Over the years, there has been a great deal of work in the use of fluorescent, colourimetric, and/or ratiometric probes for Hg²⁺ recognition. Essentially, the purpose of this review article is to give an overview of the advances made in the constructions of such probes based on the works reported in the period from 2011 to 2019. Discussion in this review work has been tailored to the kinds of fluorophore scaffolds used for the constructions of the probes reported. Selected examples of probes under each fluorophore subcategory were discussed with mentions of the typically determined parameters in an analytical sensing operation, including modulation in fluorescence intensity, optimal pH, detection limit, and association constant. The environmental and biological application ends of the probes were also touched where necessary. Important generalisations and conclusions were given at the end of the review. This review article highlights 196 references.

Responsive ruthenium complex probe for phosphorescence and time-gated luminescence detection of bisulfite

Sensitive and selective quantification of specific analytes is of great significance in analytical and environmental sciences, as well as in the food industry. Herein, we report the design, synthesis, characterization, and application of a responsive ruthenium(ii) complex probe, Ru-azo, for phosphorescence and time-gated luminescence (TGL) detection of bisulfite, an important additive in the food industry. Upon a specific nucleophilic addition reaction between bisulfite and the azo group of Ru-azo, a new ruthenium(ii) complex, Ru-SO3, was obtained, which resulted in a remarkable increase in phosphorescence intensity, allowing the bisulfite detection to be achieved. In addition, long-lived emissions of Ru-azo (τ = 258 ns) and Ru-SO3 (τ = 261 ns) also enabled the TGL detection of bisulfite in autofluorescence-rich food samples. Through theoretical computations, the photoinduced electron transfer (PET) process within the ruthenium(ii) complex was validated, which unveiled the rationality of the luminescence "off-on" response of Ru-azo to bisulfite. The probe showed advantages of good water solubility, and high sensitivity, selectivity and accuracy for responding to bisulfite, facilitating its application in phosphorescence and TGL detection of bisulfite in aqueous and food samples.

Deep-Red Fluorescent Organic Nanoparticles with High Brightness and Photostability for Super-Resolution in Vitro and in Vivo Imaging Using STED Nanoscopy

To achieve super-resolution imaging in biological research using stimulated emission depletion (STED) nanoscopy, organic luminescent materials and their corresponding fluorescent nanoparticles with high brightness and photostability are of great significance. Herein, donor-acceptor-typed DBTBT-4C8 bearing flexible alkyl chains was developed, not only to afford deep-red emission from 600 to 800 nm but also to obtain high fluorescent brightness with the absolute photoluminescence quantum yields of 25%. After that, well-defined and monodispersed spherical nanoparticles using DBTBT-4C8 with bright emission, excellent biocompatibility, and photostability, which can easily mix with amphipathic block polymers, were then produced for super-resolution in vitro and in vivo imaging using STED nanoscopy. The observations showed that in contrast to confocal microscopy with a full width at half-maximum (FWHM) value of ≈400 nm, superior resolution with a significantly improved FWHM value of only 100 nm was achieved in biomedical cell imaging, which was also used to reconstruct three-dimensional images of stained HeLa cells at an ultrahigh resolution. More importantly, by using the prepared fluorescent organic nanoparticles (FONPs) in STED nanoscopy, in vivo imaging in glass catfish with largely enhanced resolution was also successfully achieved, demonstrating that these developed deep-red FONPs here are highly suitable for super-resolution in vitro and in vivo imaging using STED nanoscopy.

Two-photon imaging of aptamer-functionalized Copolymer/TPdye fluorescent organic dots targeted to cancer cells

Fluorescent organic dots (O-dots) recently have emerged as a new class of promising contrast reagents for two-photon fluorescence (TPF) imaging. However, most of these developed two-photon absorption (TPA) O-dots have no tumor-targeting group, which hampers their wide application for targeted tumor imaging. Herein, we fabricated Sgc8c aptamer-mediated TPA O-dots as a proof-of-concept of the sensing platform for targeted imaging in live cells or deep tissues. The O-dots composed of trans-4-[p-(N, N-diethylamino)styryl]-4'-(dimethyl amino) stilbene (DEAS) emerged as TPA organic emissive cores and encapsulation by using poly (methyl methacrylate-co-methacrylic acid) (PMMA-co-MAA) as polymeric encapsulating matrix to form DEAS/PMMA-co-MAA O-dots via a co-precipitation strategy. The obtained O-dots enabled an extremely high TPA absorption cross-section, bright two-photon fluorescence (excitation at 720 nm; emission at 412 nm and 434 nm), excellent cell-permeability and high penetration depth. Sgc8c aptamer, as a protein tyrosine kinase-7 (PTK7) receptor-targetable ligand, was further anchored on the surface of O-dots to obtain DEAS/PMMA-co-MAA@Sgc8c nanoprobes by 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride (EDC)-mediated coupling reaction. Guided by Sgc8c aptamer, DEAS/PMMA-co-MAA@Sgc8c nanoprobes could be rapidly internalized into target acute lymphoblastic leukemia cells (CEM) cells with high specificity and great efficiency. It was also performed that two-photon images of TPA nanoprobes exhibited high two-photon brightness not only in target CEM cells, but also in mouse liver tissue slices even a depth of up to 210 μm. In our perception, it is highly promising that this nanoprobe provides a valuable tool for in vivo targeted imaging.

Regulating the Photophysical Property of Organic/Polymer Optical Agents for Promoted Cancer Phototheranostics

On the basis of the Jablonski diagram, the photophysical properties of optical agents are highly associated with biomedical function and efficacy. Herein, the focus is on organic/polymer optical agents and the recent progress in the main strategies for regulating their photophysical properties to achieve superior cancer diagnosis/phototheranostics applications are highlighted. Both the approaches of nanoengineering and molecular design, which can lead to optimized effectiveness of required biomedical function, are discussed.

Multicomponent Plasmonic Nanoparticles: From Heterostructured Nanoparticles to Colloidal Composite Nanostructures

Plasmonic nanostructures possessing unique and versatile optoelectronic properties have been vastly investigated over the past decade. However, the full potential of plasmonic nanostructure has not yet been fully exploited, particularly with single-component homogeneous structures with monotonic properties, and the addition of new components for making multicomponent nanoparticles may lead to new-yet-unexpected or improved properties. Here we define the term "multi-component nanoparticles" as hybrid structures composed of two or more condensed nanoscale domains with distinctive material compositions, shapes, or sizes. We reviewed and discussed the designing principles and synthetic strategies to efficiently combine multiple components to form hybrid nanoparticles with a new or improved plasmonic functionality. In particular, it has been quite challenging to precisely synthesize widely diverse multicomponent plasmonic structures, limiting realization of the full potential of plasmonic heterostructures. To address this challenge, several synthetic approaches have been reported to form a variety of different multicomponent plasmonic nanoparticles, mainly based on heterogeneous nucleation, atomic replacements, adsorption on supports, and biomolecule-mediated assemblies. In addition, the unique and synergistic features of multicomponent plasmonic nanoparticles, such as combination of pristine material properties, finely tuned plasmon resonance and coupling, enhanced light-matter interactions, geometry-induced polarization, and plasmon-induced energy and charge transfer across the heterointerface, were reported. In this review, we comprehensively summarize the latest advances on state-of-art synthetic strategies, unique properties, and promising applications of multicomponent plasmonic nanoparticles. These plasmonic nanoparticles including heterostructured nanoparticles and composite nanostructures are prepared by direct synthesis and physical force- or biomolecule-mediated assembly, which hold tremendous potential for plasmon-mediated energy transfer, magnetic plasmonics, metamolecules, and nanobiotechnology.

Environmentally benign, facile and selective recovery of gold from aqueous media: synergic role of carbon dots as green reductant and sensor towards Au3+ ions

Photoluminescent carbon dots (PL CDs) have drawn tremendous attention from researchers owing to their admirable properties and wide range of applications. Herein, highly PL nitrogen and sulfur doped carbon dots (N,S-CDs) were synthesized through a facile, green and rapid one-step microwave assisted method using goat hooves, a bio-waste and a green precursor. The structural and photophysical properties of as obtained N,S-CDs were thoroughly investigated. From the investigation, it is revealed that the N,S-CDs possess a spherical morphology with an average particle size of about 2 nm, highly amorphous nature, high functionality, negative zeta potential (-32 mV), good water-solubility, excitation dependant PL, high PL quantum yield (23.8%), nanosecond lifetime (τ _avg = 3.38 ns) and excellent storage stability for 180 days without any agglomeration. In addition, the N,S-CDs exhibit high PL stability under diverse pH conditions, wide ionic strength and resistance towards photobleaching, which are very important properties for practical applications. The N,S-CDs selectively sense Au³⁺ ions and also reduce the Au³⁺ ions to metallic gold. Hence, the N,S-CDs were successfully applied as a potential candidate for sensing of Au³⁺ and simultaneous extraction of metallic gold in aqueous media without any further reducing agents. It is a significant green way for the recovery of gold in aqueous media.

A photo-regulated aptamer sensor for spatiotemporally controlled monitoring of ATP in the mitochondria of living cells

Fluorescent aptamer sensors have shown enormous potential for intracellular imaging of small molecule metabolites. Since metabolites distribute differently at different subcellular locations and their concentrations and locations fluctuate with time, methods are needed for spatiotemporally controlled monitoring of these metabolites. Built upon previous success in temporal control of aptamer-based sensors, we herein report an aptamer sensor containing a photocleavable linker and using DQAsomes to target mitochondria for spatiotemporally controlled monitoring of ATP in the mitochondria of living cells. The photocleavable modification on the DNA ATP aptamer sensor can prevent sensor activation before reaching mitochondria and the sensor can then be activated upon light irradiation. The sensor has a detection limit of 3.7 μM and high selectivity against other nucleotides, allowing detection of ATP concentration fluctuations in mitochondria induced by Ca²⁺ or oligomycin. This work represents the first successful delivery of a DNA aptamer sensor to mitochondria, providing a new platform for targeted delivery to subcellular organelles for monitoring energy producing processes, as well as mitochondrial dysfunction-related diseases in different cells.

A photo-regulated ATP sensor coupled with cationic DQAsomes is developed for spatiotemporally controlled imaging of ATP in the mitochondria of living cells.

Anisotropic nanomaterials for shape-dependent physicochemical and biomedical applications

This review contributes towards a systematic understanding of the mechanism of shape-dependent effects on nanoparticles (NPs) for elaborating and predicting their properties and applications based on the past two decades of research. Recently, the significance of shape-dependent physical chemistry and biomedicine has drawn ever increasing attention. While there has been a great deal of effort to utilize NPs with different morphologies in these fields, so far research studies are largely localized in particular materials, synthetic methods, or biomedical applications, and have ignored the interactional and interdependent relationships of these areas. This review is a comprehensive description of the NP shapes from theory, synthesis, property to application. We figure out the roles that shape plays in the properties of different kinds of nanomaterials together with physicochemical and biomedical applications. Through systematic elaboration of these shape-dependent impacts, better utilization of nanomaterials with diverse morphologies would be realized and definite strategies would be expected for breakthroughs in these fields. In addition, we have proposed some critical challenges and open problems that need to be addressed in nanotechnology.

Impact of Protein Corona in Nanoflare-Based Biomolecular Detection and Quantification

Selective detection and precise quantification of biomolecules in intracellular settings play a pivotal role in the diagnostics and therapeutics of diseases, including various cancers and infectious epidemics. Because of this clinical relevance, nanoprobes with high sensitivity, wide tunability, and excellent biological stability have become of high demand. In particular, nanoflares based on gold nanoparticles have emerged as an attractive candidate for intracellular detection due to their efficient cellular uptake, enhanced binding affinity with complementary targets, and improved biological compatibility. However, nanoprobes, including these nanoflares, are known to be susceptible to the adsorption of proteins present in the biological environment, which leads to the formation of a so-called protein corona layer on their surface, leading to an altered targeting efficiency and cellular uptake. In this work, we leverage the nanoflares platform to demonstrate the effect of protein corona on biomolecular detection, quantification, as well as biological stability against enzymatic degradation. Nanoflares incubated in a biologically relevant concentration of serum albumin proteins (0.50 wt %) were shown to result in more than 20% signal reduction in target detection, with a decrease varying proportionally with the protein concentrations. In addition, similar signal reduction was observed for different serum proteins, and PEG backfilling was found to be ineffective in mitigating the negative impact induced by the corona formation. Furthermore, nuclease resistance in nanoflares was also severely compromised by the presence of the corona shell (∼2-fold increase in hydrolysis activity). This work demonstrates the consequences of an in situ formed protein corona layer on molecular detection/quantification and biological stability of nanoflares in the presence of nuclease enzymes, highlighting the importance of calibrating similar nanoprobes in proper biological media to improve the accuracy of molecular detection and quantification.

Surface-Engineered Gold Nanoclusters with Biological Assembly-Amplified Emission for Multimode Imaging

Here, we develop bifunctional ligand-engineered gold nanoclusters (AuNCs) as signal amplifying reporters for multimode imaging. Modified streptavidin (SA) and biotin alkyl acid-based ligands were applied to AuNCs to form AuNC-SA and AuNC-biotin. The zwitterionic ligands promoted bioassembly and avoided nonspecific adsorption. The AuNCs resisted aggregation-induced quenching and showed strong emission benefited from biological self-assembly. The engineered AuNCs featured stable emission, a large two-photon absorption cross section, long fluorescence lifetime, and good biocompatibility. Thus, cell-expressed antigen-induced protein-binding events were effectively converted into signals from the biological assemble of AuNCs. We performed a comprehensive assay of specific antigens and the cell structure, through one-photon imaging, two-photon imaging, and fluorescence lifetime imaging of AuNCs in a simple, sensitive, and reliable way.

Enabling biodegradable functional biomaterials for the management of neurological disorders

An increasing number of patients are being diagnosed with neurological diseases, but are rarely cured because of the lack of curative therapeutic approaches. This situation creates an urgent clinical need to develop effective diagnosis and treatment strategies for repair and regeneration of injured or diseased neural tissues. In this regard, biodegradable functional biomaterials provide promising solutions to meet this demand owing to their unique responsiveness to external stimulation fields, which enable neuro-imaging, neuro-sensing, specific targeting, hyperthermia treatment, controlled drug delivery, and nerve regeneration. This review discusses recent progress in the research and development of biodegradable functional biomaterials including electroactive biomaterials, magnetic materials and photoactive biomaterials for the management of neurological disorders with emphasis on their applications in bioimaging (photoacoustic imaging, MRI and fluorescence imaging), biosensing (electrochemical sensing, magnetic sensing and opical sensing), and therapy strategies (drug delivery, hyperthermia treatment, and tissue engineering). It is expected that this review will provide an insightful discussion on the roles of biodegradable functional biomaterials in the diagnosis and treatment of neurological diseases, and lead to innovations for the design and development of the next generation biodegradable functional biomaterials.

Boosting Cancer Therapy with Organelle-Targeted Nanomaterials

The ultimate goal of cancer therapy is to eliminate malignant tumors while causing no damage to normal tissues. In the past decades, numerous nanoagents have been employed for cancer treatment because of their unique properties over traditional molecular drugs. However, lack of selectivity and unwanted therapeutic outcomes have severely limited the therapeutic index of traditional nanodrugs. Recently, a series of nanomaterials that can accumulate in specific organelles (nucleus, mitochondrion, endoplasmic reticulum, lysosome, Golgi apparatus) within cancer cells have received increasing interest. These rationally designed nanoagents can either directly destroy the subcellular structures or effectively deliver drugs into the proper targets, which can further activate certain cell death pathways, enabling them to boost the therapeutic efficiency, lower drug dosage, reduce side effects, avoid multidrug resistance, and prevent recurrence. In this Review, the design principles, targeting strategies, therapeutic mechanisms, current challenges, and potential future directions of organelle-targeted nanomaterials will be introduced.

Small-molecule fluorescent probes for specific detection and imaging of chemical species inside lysosomes

In the past few years, the preparation of novel small-molecule fluorescent probes for specific detection and imaging of chemical species inside lysosomes has attracted considerable attention because of their wide applications in chemistry, biology, and medical science. This feature article summarizes the recent advances in the design and preparation of small-molecule fluorescent probes for specific detection of chemical species inside lysosomes. In addition, their properties and applications for the detection and imaging of pH, H2O2, HOCl, O2˙-, lipid peroxidation, H2S, HSO3-, thiols, NO, ONOO-, HNO, Zn2+, Cu2+, enzymes, etc. in lysosomes are discussed as well.

An aptamer-based four-color fluorometic method for simultaneous determination and imaging of alpha-fetoprotein, vascular endothelial growth factor-165, carcinoembryonic antigen and human epidermal growth factor receptor 2 in living cells

The extraordinary fluorescence quenching capability of graphene oxide (GO) was coupled to the specific recognition capability of aptamers to design a four-color fluorescent nanoprobe for multiplexed detection and imaging of tumor-associated proteins in living cells. Specifically, alpha-fetoprotein (AFP), vascular endothelial growth factor-165 (VEGF₁₆₅), carcinoembryonic antigen (CEA), and human epidermal growth factor receptor 2 (HER2) were detected. Due to strong π interaction, the fluorescence of labeled aptamers is quenched by GO. Four fluorophore-labeled aptamers that bind the tumor-associated proteins were adsorbed on GO to form the four-color nanoprobe with quenched fluorescence. The nanoprobes were internalized into cells via endocytosis, where the aptamer/GO nanoprobes bind the intracellular tumor-associated proteins. The aptamer-protein complexes thus formed detach from GO, and fluorescence recovers. Each analyte has its typical color (AFP: blue; VEGF165: green; CEA: yellow; HER2: red). As a result, simultaneous detection and imaging of multiple tumor-associated proteins in living cells were achieved. This nanoprobe has a fast response and is highly specific and biocompatible. The linear ranges for AFP, VEGF₁₆₅, CEA, and HER2 are 0.8 nM-160 nM, 0.5 nM-100 nM, 1.0 nM-200 nM, and 1.2 nM-240 nM, respectively. Detection limits were 0.45 nM for AFP, 0.30 nM for VEGF₁₆₅, 0.62 nM for CEA, and 0.96 nM for HER2. The probe allows for a fast distinction between tumor cells and normal cells via imaging. Graphical abstract Schematic presentation of the development of a four-color fluorometic method based on aptamer and graphene oxide for simultaneous detection and imaging of alpha-fetoprotein, vascular endothelial growth factor-165, carcinoembryonic antigen and human epidermal growth factor receptor 2 in living cells.

Gold Nanocluster-Decorated Nanocomposites with Enhanced Emission and Reactive Oxygen Species Generation

Ligand-protected gold nanoclusters (AuNCs) show promise for high performance in biological applications, such as imaging and therapeutics. The assembly of AuNCs with biological macromolecules represents a simple but effective approach to fine-tuning of material functionalities. Thus, these materials might enable intracellular applications of AuNCs. Herein, we prepared a new AuNC-based nanometric system through a self-assembly approach mediated by hydrophobic and electrostatic effects. We show that hydrophobic and electrostatic effects between fluorescent AuNCs with protamine and hyaluronic acid contribute to the formation of small nanocomposites with acceptable colloidal stability. More importantly, the AuNC-decorated nanocomposites show assembly enhanced emission and singlet oxygen generation. In vitro experiments showed that our nanocomposites labeled specific cells by targeting CD44 and induced cell death by producing singlet oxygen. Hence, our AuNC-decorated nanocomposites show great potential as theranostic fluorescent nanomaterials.

Sensitive, Real-Time, and In-Vivo Oxygen Monitoring for Photodynamic Therapy by Multifunctional Mesoporous Nanosensors

Real-time monitoring of oxygen consumption is beneficial to predict treatment responses and optimize therapeutic protocols for photodynamic therapy (PDT). In this work, we first demonstrate that deformable hollow mesoporous organosilica nanoparticles (HMONs) can be used to load [(Ru(dpp)₃)]Cl₂ for detecting oxygen (denoted as HMON-[(Ru(dpp)₃)]Cl₂). This nanoprobe shows significantly improved biocompatibility and high cellular uptake. In-vitro experiments demonstrate that the HMON-[(Ru(dpp)₃)]Cl₂ can sensitively detect oxygen changes between 1% and 20%. On this basis, photosensitizer chlorin e6 (Ce6) and [(Ru(dpp)₃)]Cl₂ are simultaneously loaded in the HMONs (denoted as HMON-Ce6-[(Ru(dpp)₃)]Cl₂) for real-time oxygen monitoring during photodynamic therapy. The HMON-Ce6-[(Ru(dpp)₃)]Cl₂ can reflects oxygen consumption in solution and cells in photodynamic therapy. Furthermore, the ability of the HMON-Ce6-[(Ru(dpp)₃)]Cl₂ nanosensor to monitor oxygen changes is demonstrated in tumor-bearing nude mice.

Nitrogen and chlorine co-doped carbon dots as probe for sensing and imaging in biological samples

A facile one-step hydrothermal synthesis approach was proposed to prepare nitrogen and chlorine co-doped carbon dots (CDs) using l-ornithine hydrochloride as the sole precursor. The configuration and component of CDs were characterized by transmission electron microscopy and X-ray photoelectron and Fourier transform infrared spectroscopies. The obtained CDs (Orn-CDs) with a mean diameter of 2.1 nm were well monodispersed in aqueous solutions. The as-prepared CDs exhibited a bright blue fluorescence with a high yield of 60%, good photostability and low cytotoxicity. The emission of Orn-CDs could be selectively and effectively suppressed by Fe3+. Thus, a quantitative assay of Fe3+ was realized by this nanoprobe with a detection limit of 95.6 nmol l-1 in the range of 0.3-50 µmol l-1. Furthermore, ascorbic acid could recover the fluorescence of Orn-CDs suppressed by Fe3+, owing to the transformation of Fe3+ to Fe2+ by ascorbic acid. The limit of detection for ascorbic acid was 137 nmol l-1 in the range of 0.5-10 µmol l-1. In addition, the established method was successfully applied for Fe3+ and ascorbic acid sensing in human serum and urine specimens and for imaging of Fe3+ in living cells. Orn-CD-based sensing platform showed its potential to be used for biomedicine-related study because it is cost-effective, easily scalable and can be used without additional functionalization and sample pre-treatment.

Amplified Split Aptamer Sensor Delivered Using Block Copolymer Nanoparticles for Small Molecule Imaging in Living Cells

We develop a novel amplified split aptamer sensor for highly sensitive detection and imaging of small molecules in living cells by using cationic block copolymer nanoparticles (BCNs) with entrapped fluorescent conjugated polymer as a delivery agent. The design of a split aptamer as the initiator of hybridization chain reaction (HCR) affords the possibility of enhancing the signal-to-background ratio and thus allows high-contrast imaging for small molecules with relatively weak interactions with their aptamers. The novel design of using fluorescent cationic BCNs as the nanocarrier enables efficient and self-tracking transfection of DNA probes. Results reveal that BCNs exhibit high fluorescence brightness allowing direct tracking of the delivery location. The developed amplified split aptamer sensor is shown to have high sensitivity and selectivity for in vitro quantitative detection of adenosine triphosphate (ATP) with a detection limit of 30 nM. Live cell studies show that the sensor provides a "signal on" approach for specific, high-contrast imaging of ATP. The DNA sensor based HCR system may provide a new generally applicable platform for detection and imaging of low-abundance biomarkers.

Gold nanorods decorated with graphene oxide and multi-walled carbon nanotubes for trace level voltammetric determination of ascorbic acid

An ultra-sensitive sensor is described for the voltammetric determination of ascorbic acid (AA). A glassy carbon electrode (GCE) was modified with graphene oxide (GO), multi-walled carbon nanotubes (MWCNTs) and gold nanorods (AuNRs). GO was used to prevent the aggregation of MWCNTs. The integration of positively charged AuNRs reduces the overpotential and increases the peak current of AA oxidation. Figures of merit of this sensor, typically operated at a low working potential of 0.036 V (vs. Ag/AgCl), include a low detection limit (0.85 nM), high sensitivity (7.61 μA·μM^-1·cm^-2) and two wide linear ranges (from 1 nM to 0.5 μM and from 1 μM to 8 mM). The use of GO simplifies the manufacture and results in a highly reproducible and stable sensor. It was applied to the quantification of AA in spiked serum. Graphical abstract Graphical abstract contains poor quality and small text inside the artwork. Please do not re-use the file that we have rejected or attempt to increase its resolution and re-save. It is originally poor, therefore, increasing the resolution will not solve the quality problem. We suggest that you provide us the original format. We prefer replacement figures containing vector/editable objects rather than embedded images. Preferred file formats are eps, ai, tiff and pdf.We have provided the original format with the attachments named g.tif. Graphene oxide (GO) in combination with multiwalled carbon nanotubes (MWCNTs) and gold nanorods (AuNRs) were used to construct a sensing interface with outstanding electrocatalytic performance for ascorbic acid detection.

Optical Control of Metal Ion Probes in Cells and Zebrafish Using Highly Selective DNAzymes Conjugated to Upconversion Nanoparticles

Spatial and temporal distributions of metal ions in vitro and in vivo are crucial in our understanding of the roles of metal ions in biological systems, and yet there is a very limited number of methods to probe metal ions with high space and time resolution, especially in vivo. To overcome this limitation, we report a Zn²⁺-specific near-infrared (NIR) DNAzyme nanoprobe for real-time metal ion tracking with spatiotemporal control in early embryos and larvae of zebrafish. By conjugating photocaged DNAzymes onto lanthanide-doped upconversion nanoparticles (UCNPs), we have achieved upconversion of a deep tissue penetrating NIR 980 nm light into 365 nm emission. The UV photon then efficiently photodecages a substrate strand containing a nitrobenzyl group at the 2'-OH of adenosine ribonucleotide, allowing enzymatic cleavage by a complementary DNA strand containing a Zn²⁺-selective DNAzyme. The product containing a visible FAM fluorophore that is initially quenched by BHQ1 and Dabcyl quenchers is released after cleavage, resulting in higher fluorescent signals. The DNAzyme-UCNP probe enables Zn²⁺ sensing by exciting in the NIR biological imaging window in both living cells and zebrafish embryos and detecting in the visible region. In this study, we introduce a platform that can be used to understand the Zn²⁺ distribution with spatiotemporal control, thereby giving insights into the dynamical Zn²⁺ ion distribution in intracellular and in vivo models.