Using nanoparticles to push the limits of detection

Overcoming the Low-Stability Bottleneck in the Clinical Translation of Liposomal Pressurized Metered-Dose Inhalers: A Shell Stabilization Strategy Inspired by Biomineralization

Currently, several types of inhalable liposomes have been developed. Among them, liposomal pressurized metered-dose inhalers (pMDIs) have gained much attention due to their cost-effectiveness, patient compliance, and accurate dosages. However, the clinical application of liposomal pMDIs has been hindered by the low stability, i.e., the tendency of the aggregation of the liposome lipid bilayer in hydrophobic propellant medium and brittleness under high mechanical forces. Biomineralization is an evolutionary mechanism that organisms use to resist harsh external environments in nature, providing mechanical support and protection effects. Inspired by such a concept, this paper proposes a shell stabilization strategy (SSS) to solve the problem of the low stability of liposomal pMDIs. Depending on the shell material used, the SSS can be classified into biomineralization (biomineralized using calcium, silicon, manganese, titanium, gadolinium, etc.) biomineralization-like (composite with protein), and layer-by-layer (LbL) assembly (multiple shells structured with diverse materials). This work evaluated the potential of this strategy by reviewing studies on the formation of shells deposited on liposomes or similar structures. It also covered useful synthesis strategies and active molecules/functional groups for modification. We aimed to put forward new insights to promote the stability of liposomal pMDIs and shed some light on the clinical translation of relevant products.

SERS-Based Optical Nanobiosensors for the Detection of Alzheimer's Disease

Alzheimer's disease (AD) is a leading cause of dementia, impacting millions worldwide. However, its complex neuropathologic features and heterogeneous pathophysiology present significant challenges for diagnosis and treatment. To address the urgent need for early AD diagnosis, this review focuses on surface-enhanced Raman scattering (SERS)-based biosensors, leveraging the excellent optical properties of nanomaterials to enhance detection performance. These highly sensitive and noninvasive biosensors offer opportunities for biomarker-driven clinical diagnostics and precision medicine. The review highlights various types of SERS-based biosensors targeting AD biomarkers, discussing their potential applications and contributions to AD diagnosis. Specific details about nanomaterials and targeted AD biomarkers are provided. Furthermore, the future research directions and challenges for improving AD marker detection using SERS sensors are outlined.

Enhancing the electrocatalytic activity of palladium nanocluster tags by selective introduction of gold atoms: Application for a wound infection biomarker detection

In this work, an unprecedented study exploring the role that slight changes into the Pd/Au proportion have in the electrocatalytic activity of bimetallic Pd-AuNPs toward the oxygen reduction reaction (ORR) is conducted. In particular, a careful control of the amount of Au atoms introduced in the cluster and the evaluation of the optimum Pd:Au ratio for getting the maximum catalytic activity is performed for the first time. First, PdNPs are synthesized by alcohol reduction in the presence of polyvinylpyrrolidone, and gold atoms are selectively introduced on vertex or corner positions of the cluster in different amounts following a galvanic substitution procedure. Average elemental analysis done relying on EDX spectroscopy allows to evaluate the Pd:Au ratio in the Pd-AuNPs obtained. Lineal sweep voltammetry and chronoamperometry are used for the evaluation of the Pd-AuNPs electrocatalytic activity toward ORR at a neutral pH compared to PdNPs and AuNPs alone. Our results indicate that, the synergy between both metals is strongly enhanced when the amount of gold is controlled and occupies the more reactive positions of the cluster, reaching a maximum activity for the NPs containing a 30% of gold, while an excess of this metal leads to a decrease in such activity, as a shelter of the PdNPs is achieved. Chronoamperometric analysis allows the quantification of the optimal Pd-AuNPs at over 6 × 10⁹ NPs/mL levels. Such optimal Pd-AuNPs were used as tags, taking advantage of the bio-functionalities of gold present in the cluster, in a proof-of-concept electrochemical immunosensor for the detection of hyaluronidase wound infection biomarker, using magnetic beads as platforms. Hyaluronidase was detected at levels as low as 50 ng/mL (0.02 U/mL; 437 U/mg) with good reproducibility (RSD below 8%) and selectivity (evaluated against bovine serum albumin, immunoglobulin G and lysozyme). The low matrix effects inherent to the use of magnetic bead platforms allowed us to discriminate between wound exudates with both sterile and infected ulcers without sample pre-treatment. This novel electrocatalytic immunoassay has the advantage, over common methods for NP tags electrochemical detection, of the signal generation in the same neutral medium where the immunoassay takes place (10 mM PBS pH 7.4), avoiding the use of additional and hazardous reagents, bringing it closer to their use as point-of-care devices. Overall, our findings may be of great interest not only for biosensing, but also for applications such as energy converting on fuel cells, in which the ORR has a pivotal role.

Development and validation of an HPLC-fluorescence method for the quantification of IR780-oleyl dye in lipid nanoparticles

A reversed-phase (RP) high-performance liquid chromatography (HPLC) method for the content determination of IR780-oleyl (IRO) dye in lipid nanoparticles was developed and validated. Chromatographic separation was performed on a RP C18 column with a gradient program of water and acetonitrile both with 0.1% (v/v) TFA, at a flow rate of 1.0mL/min and a total run of 21min. IRO dye detection was made by fluorescence at emission wavelength of 773nm (excitation wavelength: 744nm). According to ICH guidelines, the developed method was shown to be specific, linear in the range 3-8μg/mL (R²=0.9998), precise at the intra-day and inter-day levels as reflected by the coefficient of variation (CV≤1.98%) at three different concentrations (4, 6 and 8 μg/mL) and accurate, with recovery rates between 98.2-101.6% and 99.2-100.5%. The detection and quantitation limits were 0.41 and 1.24μg/mL, respectively. Stability studies of sample processing showed that IRO dye was stable after 24h in the autosampler or after three freeze/thaw cycles. Combined with fluorescence measurements, the developed method was successfully applied to optimize the loading capacity of IRO dye in the core of lipid nanoparticles.

Ultrasensitive rapid detection of human serum antibody biomarkers by biomarker-capturing viral nanofibers

Candida albicans (C. albicans) infection causes high mortality rates within cancer patients. Due to the low sensitivity of the current diagnosis systems, a new sensitive detection method is needed for its diagnosis. Toward this end, here we exploited the capability of genetically displaying two functional peptides, one responsible for recognizing the biomarker for the infection (antisecreted aspartyl proteinase 2 IgG antibody) in the sera of cancer patients and another for binding magnetic nanoparticles (MNPs), on a single filamentous fd phage, a human-safe bacteria-specific virus. The resultant phage is first decorated with MNPs and then captures the biomarker from the sera. The phage-bound biomarker is then magnetically enriched and biochemically detected. This method greatly increases the sensitivity and specificity of the biomarker detection. The average detection time for each serum sample is only about 6 h, much shorter than the clinically used gold standard method, which takes about 1 week. The detection limit of our nanobiotechnological method is approximately 1.1 pg/mL, about 2 orders of magnitude lower than that of the traditional antigen-based method, opening up a new avenue to virus-based disease diagnosis.

Segmented flow reactors for nanocrystal synthesis

In the past decade microreactors have emerged as a compelling technology for the highly controlled synthesis of colloidal nanocrystals, offering multiple advantages over conventional batch synthesis methods (including improved levels of control, reproducibility, and automation). Initial work in the field employed simple continuous phase reactors that manipulate miscible streams of a single reagent phase. Recently, however, there has been increasing interest in segmented flow reactors that use an immiscible fluid to divide the reagent phase into discrete slugs or droplets. Key advantages of segmented flow include the elimination of velocity dispersion (a significant cause of polydispersity) and greatly reduced susceptibility to reactor fouling. In this progress report we review the operation of segmented flow microreactors, their application to the controlled synthesis of nanocrystals, and some of the principal challenges that must be addressed before they can become a mainstream technology for the controlled production of nanomaterials.

Luminescent Iridium(III)-Containing Block Copolymers: Self-Assembly into Biotin-Labeled Micelles for Biodetection Assays

Luminescent polymers containing Ir(ppy)₂(bpy) PF₆ complexes, biocompatible poly(ethylene glycol) (PEG) chains, and biotin moieties were synthesized via ring-opening metathesis polymerization (ROMP). Their self-assembly in water into micelles resulted in an increased quantum yield compared to open polymer chains in acetonitrile, which is likely due to core rigidity and desolvation. Streptavidin coated magnetic beads were employed to analyze the binding ability of these micelles. The positioning of the molecular recognition moiety biotin within the polymer chain had a very significant effect on the availability of biotin on the micelle surface and the ability of the micelles to bind to streptavidin. Simply attaching biotin to the end of the ROMP polymer yielded micelles in which the biotin units were shielded by the PEG chains, whereas the synthesis of a new ROMP monomer containing biotin at the end of the PEG chains resulted in improved surface availability of the biotin group. Preliminary experiments in which streptavidin was microcontact-printed onto functionalized glass coverslips also indicated specific binding between the micelles and streptavidin and further demonstrated the potential of these micelle systems to function as luminescent probes in solid-phase biodetection assays.

Surface functionalization chemistries on highly sensitive silica-based sensor chips

The surfaces of silica-based sensor chips, designed for evanescent-field-coupled waveguide-mode sensors, were functionalized using various surface chemistries. The immobilization of molecular entities on the functionalized silica surfaces was monitored using various microscopic techniques (scanning electron, fluorescence, and atomic force microscopies). Further, gold nanoparticle-based signal enhancement analyses were performed with protein conjugation on different functionalized surfaces using a waveguide-mode sensor. Based on these analyses, the sensor surfaces modified with glutaraldehyde (Glu) and carbonyldiimidazole were found to be good for molecules of different sizes. In addition, it can be inferred that the Glu-modified surface may be suitable for small molecules with diameters around 5 nm owing to its surface roughness. The modified surface with carbonyldiimidazole is suitable for the direct immobilization of larger molecules especially for biomolecular assemblies without intermediate chemical modifications.

Controlling bubbles using bubbles--microfluidic synthesis of ultra-small gold nanocrystals with gas-evolving reducing agents

Microfluidic wet-chemical synthesis of nanoparticles is a growing area of research in chemical microfluidics, enabling the development of continuous manufacturing processes that overcome the drawbacks of conventional batch-based synthesis methods. The synthesis of ultra-small (<5 nm) metallic nanocrystals is an interesting area with many applications in diverse fields, but is typically very challenging to accomplish in a microfluidics-based system due to the use of a strong gas-evolving reducing agent, aqueous sodium borohydride (NaBH(4)), which causes uncontrolled out-gassing and bubble formation, flow disruption and ultimately reactor failure. Here we present a simple method, rooted in the concepts of multiphase mass transfer that completely overcomes this challenge-we simply inject a stream of inert gas bubbles into our channels that essentially capture the evolving gas from the reactive aqueous solution, thereby preventing aqueous dissolved gas concentration from reaching the solubility threshold for bubble nucleation. We present a simple model for coupled mass transfer and chemical reaction that adequately captures device behaviour. We demonstrate the applicability of our method by synthesizing ultra-small gold nanocrystals (<5 nm); the quality of nanocrystals thus synthesized is further demonstrated by their use in an off-chip synthesis of high-quality gold nanorods. This is a general approach that can be extended to a variety of metallic nanomaterials.

Noble metal nanoparticles for biosensing applications

In the last decade the use of nanomaterials has been having a great impact in biosensing. In particular, the unique properties of noble metal nanoparticles have allowed for the development of new biosensing platforms with enhanced capabilities in the specific detection of bioanalytes. Noble metal nanoparticles show unique physicochemical properties (such as ease of functionalization via simple chemistry and high surface-to-volume ratios) that allied with their unique spectral and optical properties have prompted the development of a plethora of biosensing platforms. Additionally, they also provide an additional or enhanced layer of application for commonly used techniques, such as fluorescence, infrared and Raman spectroscopy. Herein we review the use of noble metal nanoparticles for biosensing strategies—from synthesis and functionalization to integration in molecular diagnostics platforms, with special focus on those that have made their way into the diagnostics laboratory.

Aptamer-conjugated nanomaterials and their applications

The combination of aptamers with novel nanomaterials, including nanomaterial-based aptamer bioconjugates has attracted considerable interest and has led to a wide variety of applications. In this review, we discuss how a variety of nanomaterials, including gold, silica and magnetic nanoparticles, as well as carbon nanotubes, hydrogels, liposomes and micelles, have been used to functionalize aptamers for a variety of applications. These aptamer functionalized materials have led to advances in amplified biosensing, cancer cell-specific recognition, high-efficiency separation, and targeted drug delivery.

Thin gold film-assisted fluorescence spectroscopy for biomolecule sensing

We present a configuration for fluorescence spectroscopy that exploits the optical properties of semitransparent gold films and widely available instrumentation. This method enables monitoring of biomolecule interactions with small molecules tethered on substrates in multicomponent environments. The neurotransmitter serotonin (5-hydroxytryptamine) was covalently attached to self-assembled monolayers on thin gold films at low density to facilitate antibody recognition. Protein-binding studies were performed in a fluorescently labeled immunoassay format. We find that the use of this method enables evaluation of nonspecific binding and relative quantification of specific binding between competing binding partners. This fluorescence spectroscopy technique has the potential to assess biosensor or medical device responses in complex biological matrices.

Fluorescent nanoparticle probes for imaging of cancer

Fluorescent nanoparticles (FNPs) have received immense popularity in cancer imaging in recent years because of their attractive optical properties. In comparison to traditional organic-based fluorescent dyes and fluorescent proteins, FNPs offer much improved sensitivity and photostability. FNPs in certain size range have a strong tendency to enter and retain in solid tumor tissue with abnormal (leaky) vasculature--a phenomenon known as Enhanced Permeation and Retention (EPR) effect, advancing their use for in vivo tumor imaging. Furthermore, large surface area of FNPs and their usual core-shell structure offer a platform for designing and fabricating multimodal/multifunctional nanoparticles (MMNPs). For effective cancer imaging, often the optical imaging modality is integrated with other nonoptical-based imaging modalities such as MRI, X-ray, and PET, thus creating multimodal nanoparticle (NP)-based imaging probes. Such multimodal NP probes can be further integrated with therapeutic drug as well as cancer targeting agent leading to multifunctional NPs. Biocompatibility of FNPs is an important criterion that must be seriously considered during FNP design. NP composition, size, and surface chemistry must be carefully selected to minimize potential toxicological consequences both in vitro and in vivo. In this article, we will mainly focus on three different types of FNPs: dye-loaded NPs, quantum dots (Qdots), and phosphores; briefly highlighting their potential use in translational research.

Multifunctional nanoparticles as simulants for a gravimetric immunoassay

Immunoassays are important tools for the rapid detection and identification of pathogens, both clinically and in the research laboratory. An immunoassay with the potential for the detection of influenza was developed and tested using hemagglutinin (HA), a commonly studied glycoprotein found on the surface of influenza virions. Gold nanoparticles were synthesized, which present multiple peptide epitopes, including the HA epitope, in order to increase the gravimetric response achieved with the use of a QCM immunosensor for influenza. Specifically, epitopes associated with HA and FLAG peptides were affixed to gold nanoparticles by a six-mer PEG spacer between the epitope and the terminal cysteine. The PEG spacer was shown to enhance the probability for interaction with antibodies by increasing the distance the epitope extends from the gold surface. These nanoparticles were characterized using thermogravimetric analysis, transmission electron microscopy, matrix-assisted laser desorption/ionization-time of flight, and (1)H nuclear magnetic resonance analysis. Anti-FLAG and anti-HA antibodies were adhered to the surface of a QCM, and the response of each antibody upon exposure to HA, FLAG, and dual functionalized nanoparticles was compared with binding of Au-tiopronin nanoparticles and H5 HA proteins from influenza virus (H5N1). Results demonstrate that the immunoassay was capable of differentiating between nanoparticles presenting orthogonal epitopes in real-time with minimal nonspecific binding. The detection of H5 HA protein demonstrates the logical extension of using these nanoparticle mimics as a safe positive control in the detection of influenza, making this a vital step in improving influenza detection methodology.