Fully Self-Assembled Silica Nanoparticle-Semiconductor Quantum Dot Supra-Nanoparticles and Immunoconjugates for Enhanced Cellular Imaging by Microscopy and Smartphone Camera

Smartphones as a platform for molecular analysis: concepts, methods, devices and future potential

Over the past 15 years, smartphones have had a transformative effect on everyday life. These devices also have the potential to transform molecular analysis over the next 15 years. The cameras of a smartphone, and its many additional onboard features, support optical detection and other aspects of engineering an analytical device. This article reviews the development of smartphones as platforms for portable chemical and biological analysis. It is equal parts conceptual overview, technical tutorial, critical summary of the state of the art, and outlook on how to advance smartphones as a tool for analysis. It further discusses the motivations for adopting smartphones as a portable platform, summarizes their enabling features and relevant optical detection methods, then highlights complementary technologies and materials such as 3D printing, microfluidics, optoelectronics, microelectronics, and nanoparticles. The broad scope of research and key advances from the past 7 years are reviewed as a prelude to a perspective on the challenges and opportunities for translating smartphone-based lab-on-a-chip devices from prototypes to authentic applications in health, food and water safety, environmental monitoring, and beyond. The convergence of smartphones with smart assays and smart apps powered by machine learning and artificial intelligence holds immense promise for realizing a future for molecular analysis that is powerful, versatile, democratized, and no longer just the stuff of science fiction.

Dextran-Encapsulated Nanoparticles and Super-Nanoparticle Assemblies: Preparation from Quantum Dots, Fluorescent Polymers, and Magnetic Nanoparticles for Application to Cellular Immunolabeling

Nanoparticles (NPs) continue to be developed as labels for bioanalysis and imaging due to their small size and, in many cases, emergent properties such as photoluminescence (PL) and superparamagnetism. Some applications stand to benefit from amplification of the advantageous properties of a NP, but this amplification is not a simple matter of scaling for size-dependent properties. One promising approach to amplification is, therefore, to assemble many copies of a NP into a larger but still nanoscale and colloidal entity. Here, we use multiple types of hydrophobic nanocrystal to show that amphiphilic dextran is a versatile material for the preparation and surface functionalization of such super-NP assemblies: CdSe/CdS/ZnS quantum dots (QDs), InP/ZnS QDs, and Si QDs; iron oxide magnetic NPs (MNPs); composites of QDs and MNPs; and composites of QDs and MNPs with fluorene-based and phenylenevinylene-based conjugated polymers. The amphiphilic dextran was also useful for the preparation of conjugated polymer NPs (CPNs) without the inclusion of inorganic nanocrystals. The prepared super-NPs and CPNs were characterized, physically and photophysically, at both the ensemble and the single-particle levels. Per colloidal entity, the super-QDs were orders of magnitude brighter than the individual QDs. This enhancement enabled assemblies of nominally more benign InP/ZnS and Si QDs to be competitive alternative materials to CdSe/CdS/ZnS QDs, which are normally much brighter when compared as individual nanocrystals. The dextran functionalization imparted low nonspecific binding and enabled the use of tetrameric antibody complexes (TACs) for simple and selective immunolabeling of cells with all of the prepared super-NP, CPN, and composite materials. Labeling with the super-QDs provided significantly enhanced PL signals, the super-MNPs enabled magnetic pull-down of cells, and both capabilities were concurrently available with composite assemblies. Overall, this study demonstrates that the preparatory method and functional benefits of amphiphilic dextran extend to a range of hydrophobic materials and combinations thereof. There is strong potential for assembling a diverse set of property-amplified designer labels that are ready-made for in vitro applications in bioanalysis and imaging.

Supra-Quantum Dot Assemblies to Maximize Color-Based Multiplexed Fluorescence Detection with a Smartphone Camera

Photoluminescence (PL) imaging and bioanalysis with smartphone-based devices are of growing interest for point-of-care/point-of-need diagnostics. Strategies for maximizing sensitivity have been explored in this context, but color multiplexing has been very limited, with its maximum level unexplored. Here, we evaluated color multiplexing with smartphone-based PL imaging by using supra-nanoparticle assemblies of quantum dots (supra-QDs). These materials were prepared as composite colors that were tailored to the red-green-blue (RGB) color space of smartphone cameras by coassembling different ratios of R-, G-, and B-emitting QDs on a silica nanoparticle scaffold. The supra-QDs were characterized and used to label cell-sized objects that were measured under flow with a smartphone-based device. Each color followed an approximately linear trajectory in the RGB space, and training of support vector machine models enabled color classification with overall accuracies ≥87% for 10-color multiplexing and better accuracies for fewer colors. Most misclassification occurred at low signal levels, such that establishing a nonclassifiable zone near the origin of RGB color space improved the overall 10-color classification accuracy to ≥94%. Similar improvements in accuracy with greater retention of data were possible with a probabilistic rather than a radial threshold. Simulations that were parameterized by experimental data suggested that ≥14-color multiplexing with accuracies ≥90% should be possible with an optimized supra-QD color set. This study is an important foundation for advancing RGB color-based multiplexing for imaging and analyses with smartphone cameras and related charge-coupled device and CMOS color image sensor technologies.

Emerging trends in nanomaterial design for the development of point-of-care platforms and practical applications

Nanomaterials and nanotechnology offer promising opportunities in point-of-care (POC) diagnostics and therapeutics due to their unique physical and chemical properties. POC platforms aim to provide rapid and portable diagnostic and therapeutic capabilities at the site of patient care, offering cost-effective solutions. Incorporating nanomaterials with distinct optical, electrical, and magnetic properties can revolutionize the POC industry, significantly enhancing the effectiveness and efficiency of diagnostic and theragnostic devices. By leveraging nanoparticles and nanofibers in POC devices, nanomaterials have the potential to improve the accuracy and speed of diagnostic tests, making them more practical for POC settings. Technological advancements, such as smartphone integration, imagery instruments, and attachments, complement and expand the application scope of POCs, reducing invasiveness by enabling analysis of various matrices like saliva and breath. These integrated testing platforms facilitate procedures without compromising diagnosis quality. This review provides a summary of recent trends in POC technologies utilizing nanomaterials and nanotechnologies for analyzing disease biomarkers. It highlights advances in device development, nanomaterial design, and their applications in POC. Additionally, complementary tools used in POC and nanomaterials are discussed, followed by critical analysis of challenges and future directions for these technologies.

Tetrameric Antibody Complexes and Affinity Tag Peptides for the Selective Immobilization and Imaging of Single Quantum Dots

Colloidal semiconductor quantum dots (QDs) are of widespread interest as fluorescent labels for bioanalysis and imaging applications. Single-particle measurements have proven to be a very powerful tool for better understanding the fundamental properties and behaviors of QDs and their bioconjugates; however, a recurring challenge is the immobilization of QDs in a solution-like environment that minimizes interactions with a bulk surface. Immobilization strategies for QD-peptide conjugates are particularly underdeveloped within this context. Here, we present a novel strategy for the selective immobilization of single QD-peptide conjugates using a combination of tetrameric antibody complexes (TACs) and affinity tag peptides. A glass substrate is modified with an adsorbed layer of concanavalin A (ConA) that binds a subsequent layer of dextran that minimizes nonspecific binding. A TAC with anti-dextran and anti-affinity tag antibodies binds to the dextran-coated glass surface and to the affinity tag sequence of QD-peptide conjugates. The result is spontaneous and sequence-selective immobilization of single QDs without any chemical activation or cross-linking. Controlled immobilization of multiple colors of QDs is possible using multiple affinity tag sequences. Experiments confirmed that this approach positions the QD away from the bulk surface. The method supports real-time imaging of binding and dissociation, measurements of Förster resonance energy transfer (FRET), tracking of dye photobleaching, and detection of proteolytic activity. We anticipate that this immobilization strategy will be useful for studies of QD-associated photophysics, biomolecular interactions and processes, and digital assays.

Passion fruit-inspired dendritic mesoporous silica nanospheres-enriched quantum dots coupled with magnetism-controllable aptasensor enable sensitive detection of ochratoxin A in food products

Ochratoxin A (OTA) is a powerful mycotoxin present in a variety of food products, and its detection is important for human health. Here, a fluorescent aptasensor is reported for sensitive OTA determination. Specifically, the surface of bio-inspired passion fruit-like dendritic mesoporous silica nanospheres-enriched quantum dots (MSNQs-apt) was first modified with the OTA aptamer as the recognition unit and fluorescence emitter, while the aptamer-complementary DNA (MNPs-cDNA) was linked with the magnetic nanoparticles (MNPs) as the separation element. In the range of 2.56 pg/mL to 8 ng/mL, the proposed aptasensor exhibited satisfactory linearity and a detection limit of 1.402 pg/mL. The developed aptasensor achieved recoveries of 90.98-103.20% and 94.33-107.57 % in red wine and wheat flour samples, respectively. By simply replacing the aptamer, this aptasensor can be easily extended to detection of other analytes, suggesting its potential as a universal detection platform for mycotoxins in food products.

Dextran-Functionalized Super-nanoparticle Assemblies of Quantum Dots for Enhanced Cellular Immunolabeling and Imaging

Colloidal semiconductor quantum dots (QDs) are a popular material for applications in bioanalysis and imaging. Although individual QDs are bright, some applications benefit from the use of even brighter materials. One approach to achieve higher brightness is to form super-nanoparticle (super-NP) assemblies of many QDs. Here, we present the preparation, characterization, and utility of dextran-functionalized super-NP assemblies of QDs. Amphiphilic dextran was synthesized and used to encapsulate many hydrophobic QDs via a simple emulsion-based method. The resulting super-NP assemblies or "super-QDs" had hydrodynamic diameters of ca. 90-160 nm, were characterized at the ensemble and single-particle levels, had orders-of-magnitude superior brightness compared to individual QDs, and were non-blinking. Additionally, binary mixtures of red, green, and blue (RGB) colors of QDs were used to prepare super-QDs, including colors difficult to obtain from individual QDs (e.g., magenta). Tetrameric antibody complexes (TACs) enabled simple antibody conjugation for selective cellular immunolabeling and imaging with both an epifluorescence microscope and a smartphone-based platform. The technical limitations of the latter platform were overcome by the increased per-particle brightness of the super-QDs, and the super-QDs outperformed individual QDs in both cases. Overall, the super-QDs are a very promising material for bioanalysis and imaging applications where brightness is paramount.

Computational Portable Microscopes for Point-of-Care-Test and Tele-Diagnosis

In bio-medical mobile workstations, e.g., the prevention of epidemic viruses/bacteria, outdoor field medical treatment and bio-chemical pollution monitoring, the conventional bench-top microscopic imaging equipment is limited. The comprehensive multi-mode (bright/dark field imaging, fluorescence excitation imaging, polarized light imaging, and differential interference microscopy imaging, etc.) biomedical microscopy imaging systems are generally large in size and expensive. They also require professional operation, which means high labor-cost, money-cost and time-cost. These characteristics prevent them from being applied in bio-medical mobile workstations. The bio-medical mobile workstations need microscopy systems which are inexpensive and able to handle fast, timely and large-scale deployment. The development of lightweight, low-cost and portable microscopic imaging devices can meet these demands. Presently, for the increasing needs of point-of-care-test and tele-diagnosis, high-performance computational portable microscopes are widely developed. Bluetooth modules, WLAN modules and 3G/4G/5G modules generally feature very small sizes and low prices. And industrial imaging lens, microscopy objective lens, and CMOS/CCD photoelectric image sensors are also available in small sizes and at low prices. Here we review and discuss these typical computational, portable and low-cost microscopes by refined specifications and schematics, from the aspect of optics, electronic, algorithms principle and typical bio-medical applications.

A toxicological profile of silica nanoparticles

Humans are regularly exposed to silica nanoparticles in environmental and occupational contexts, and these exposures have been implicated in the onset of adverse health effects. Existing reviews on silica nanoparticle toxicity are few and not comprehensive. There are natural and synthetic sources by which crystalline and amorphous silica nanoparticles are produced. These processes influence physiochemical properties, which are factors that can dictate toxicological effects. Toxicological assessment includes exposure scenario (e.g. environmental, occupational), route of exposure, toxicokinetics, and toxicodynamics. Broader considerations include pathology, risk assessment, regulation, and treatment after injury. This review aims to consolidate the most relevant and up-to-date research in these areas to provide an exhaustive toxicological profile of silica nanoparticles.

Voltammetric Sensor Based on SeO2 Nanoparticles and Surfactants for Indigo Carmine Determination

Indigo carmine is a widely used colorant in the food and pharmaceutical industry a high concentration of which can lead to a wide range of negative effects on human health. Therefore, colorant contents have to be strictly controlled. SeO₂-nanoparticle-modified glassy carbon electrodes (GCE) have been developed as a voltammetric sensor for indigo carmine. Various types and concentrations of surfactants have been used as reagents for the stabilization of SeO₂ nanoparticle dispersions and as electrode surface co-modifiers. An amount of 1.0 mM cationic cetylpyridinium bromide (CPB) provides the best response of the indigo carmine on the modified electrode. The electrodes were characterized by cyclic voltammetry, chronoamperometry, and electrochemical impedance spectroscopy (EIS). SeO₂ nanoparticle–CPB-modified electrodes show 4.2-fold higher electroactive area vs. GCE as well as a dramatic 5043-fold decrease in the electron transfer resistance indicating effectivity of the modifier developed. The surface-controlled electrooxidation of indigo carmine proceeds irreversibly (α_a = 0.46) with the participation of two electrons and two protons. A linear dynamic range of 0.025–1.0 and 1.0–10 µM of indigo carmine were obtained with the detection and quantification limits of 4.3 and 14.3 nM, respectively. The practical applicability of the sensor was successfully shown on the pharmaceutical dosage forms.

Nano to rescue: repository of nanocarriers for targeted drug delivery to curb breast cancer

Breast cancer is a heterogeneous disease with different intrinsic subtypes. The conventional treatment of surgical resection, chemotherapy, immunotherapy and radiotherapy has not shown significant improvement in the survival rate of breast cancer patients. The therapeutics used cause bystander toxicities deteriorating healthy tissues. The breakthroughs of nanotechnology have been a promising feat in selective targeting of tumor site thus increasing the therapeutic gain. By the application of nanoenabled carriers, nanomedicines ensure targeted delivery, stability, enhanced cellular uptake, biocompatibility and higher apoptotic efficacy. The present review focuses on breakthrough of nanoscale intervention in targeted drug delivery as novel class of therapeutics. Nanoenabled carriers like polymeric and metallic nanoparticles, dendrimers, quantum dots, liposomes, solid lipid nanoparticles, carbon nanotubes, drug-antibody conjugates and exosomes revolutionized the targeted therapeutic delivery approach. These nanoassemblies have shown additional effect of improving the solubility of drugs such as paclitaxel, reducing the dose and toxicity. The present review provides an insight on the different drug conjugates employed/investigated to curb breast cancer using nanocarrier mediated targeted drug delivery. However, identification of appropriate biomarkers to target, clearer insight of the biological processes, batch uniformity, reproducibility, nanomaterial toxicity and stabilities are the hurdles faced by nanodrugs. The potential of nano-therapeutics delivery necessitates the agglomerated efforts of research community to bridge the route of nanodrugs for scale-up, commercialization and clinical applications.

Prototype Smartphone-Based Device for Flow Cytometry with Immunolabeling via Supra-nanoparticle Assemblies of Quantum Dots

Methods for the detection, enumeration, and typing of cells are important in many areas of research and healthcare. In this context, flow cytometers are a widely used research and clinical tool but are also an example of a large and expensive instrument that is limited to specialized laboratories. Smartphones have been shown to have excellent potential to serve as portable and lower-cost platforms for analyses that would normally be done in a laboratory. Here, we developed a prototype smartphone-based flow cytometer (FC). This compact 3D-printed device incorporated a laser diode and a microfluidic flow cell and used the built-in camera of a smartphone to track immunofluorescently labeled cells in suspension and measure their color. This capability was enabled by high-brightness supra-nanoparticle assemblies of colloidal semiconductor quantum dots (SiO₂@QDs) as well as a support vector machine (SVM) classification algorithm. The smartphone-based FC device detected and enumerated target cells against a background of other cells, simultaneously and selectively counted two different cell types in a mixture, and used multiple colors of SiO₂@QD-antibody conjugates to screen for and identify a particular cell type. The potential limits of multicolor detection are discussed alongside ideas for further development. Our results suggest that innovations in materials and engineering should enable eventual smartphone-based FC assays for clinical applications.

Wide visible-range activatable fluorescence ZnSe:Eu3+/Mn2+@ZnS quantum dots: local atomic structure order and application as a nanoprobe for bioimaging

The development of QDs-based fluorescent bionanoprobe for cellular imaging fundamentally relies upon the precise knowledge of particle-cell interaction, optical properties of QDs inside and outside of the cell, movement of a particle in and out of the cell, and the fate of particle. We reported engineering and physicochemical characterization of water-dispersible Eu³⁺/Mn²⁺ co-doped ZnSe@ZnS core/shell QDs and studied their potential as a bionanoprobe for biomedical applications, evaluating their biocompatibility, fluorescence behaviour by CytoViva dual mode fluorescence imaging, time-dependent uptake, endocytosis and exocytosis in RAW 264.7 macrophages. The oxidation state and local atomic structure of the Eu dopant studied by X-ray absorption fine structure (XAFS) analysis manifested that the Eu³⁺ ions occupied sites in both ZnSe and ZnS lattices for the core/shell QDs. A novel approach was developed to relieve the excitation constraint of wide bandgap ZnSe by co-incorporation of Eu³⁺/Mn²⁺ codopants, enabling the QDs to be excited at a wide UV-visible range. The QDs displayed tunable emission colors by a gradual increase in Eu³⁺ concentration at a fixed amount of Mn²⁺, systematically enhancing the Mn²⁺ emission intensity via energy transfer from the Eu³⁺ to Mn²⁺ ion. The ZnSe:Eu³⁺/Mn²⁺@ZnS QDs presented high cell viability above 85% and induced no cell activation. The detailed analyses of QDs-treated cells by dual mode fluorescence CytoViva microscopy confirmed the systematic color-tunable fluorescence and its intensity enhances as a function of incubation time. The QDs were internalized by the cells predominantly via macropinocytosis and other lipid raft-mediated endocytic pathways, retaining an efficient amount for 24 h. The unique color tunability and consistent high intensity emission make these QDs useful for developing a multiplex fluorescent bionanoprobe, activatable in wide-visible region.

Advances and Challenges of Fluorescent Nanomaterials for Synthesis and Biomedical Applications

With the rapid development of nanotechnology, new types of fluorescent nanomaterials (FNMs) have been springing up in the past two decades. The nanometer scale endows FNMs with unique optical properties which play a critical role in their applications in bioimaging and fluorescence-dependent detections. However, since low selectivity as well as low photoluminescence efficiency of fluorescent nanomaterials hinders their applications in imaging and detection to some extent, scientists are still in search of synthesizing new FNMs with better properties. In this review, a variety of fluorescent nanoparticles are summarized including semiconductor quantum dots, carbon dots, carbon nanoparticles, carbon nanotubes, graphene-based nanomaterials, noble metal nanoparticles, silica nanoparticles, phosphors and organic frameworks. We highlight the recent advances of the latest developments in the synthesis of FNMs and their applications in the biomedical field in recent years. Furthermore, the main theories, methods, and limitations of the synthesis and applications of FNMs have been reviewed and discussed. In addition, challenges in synthesis and biomedical applications are systematically summarized as well. The future directions and perspectives of FNMs in clinical applications are also presented.

Synthesis and Application of Silica-Coated Quantum Dots in Biomedicine

Quantum dots (QDs) are semiconductor nanoparticles with outstanding optoelectronic properties. More specifically, QDs are highly bright and exhibit wide absorption spectra, narrow light bands, and excellent photovoltaic stability, which make them useful in bioscience and medicine, particularly for sensing, optical imaging, cell separation, and diagnosis. In general, QDs are stabilized using a hydrophobic ligand during synthesis, and thus their hydrophobic surfaces must undergo hydrophilic modification if the QDs are to be used in bioapplications. Silica-coating is one of the most effective methods for overcoming the disadvantages of QDs, owing to silica's physicochemical stability, nontoxicity, and excellent bioavailability. This review highlights recent progress in the design, preparation, and application of silica-coated QDs and presents an overview of the major challenges and prospects of their application.

In Vitro Cellular Uptake Studies of Self-Assembled Fluorinated Nanoparticles Labelled with Antibodies

Nanoparticles (NPs) functionalized with antibodies (Abs) on their surface are used in a wide range of bioapplications. Whereas the attachment of antibodies to single NPs to trigger the internalization in cells via receptor-mediated endocytosis has been widely studied, the conjugation of antibodies to larger NP assemblies has been much less explored. Taking into account that NP assemblies may be advantageous for some specific applications, the possibility of incorporating targeting ligands is quite important. Herein, we performed the effective conjugation of antibodies onto a fluorescent NP assembly, which consisted of fluorinated Quantum Dots (QD) self-assembled through fluorine-fluorine hydrophobic interactions. Cellular uptake studies by confocal microscopy and flow cytometry revealed that the NP assembly underwent the same uptake procedure as individual NPs; that is, the antibodies retained their targeting ability once attached to the nanoassembly, and the NP assembly preserved its intrinsic properties (i.e., fluorescence in the case of QD nanoassembly).