A "chemical nose" biosensor for detecting proteins in complex mixtures

Detection of proteins with ascorbic acid-capped gold nanoparticles: a simple and highly sensitive colorimetric assay

We report a simple and highly sensitive colorimetric method for the detection and quantification of proteins, based on the aggregation of ascorbic acid (AA) capped gold nanoparticles (AuNPs) by proteins. The interactions between our AuNPs and nine different proteins of various sizes and shapes (cytochrome C (12 kDa), lysozyme (14.3 kDa), myoglobin (17 kDa), human serum albumin (66 kDa), bovine serum albumin (66.4 kDa), human transferrin (80 kDa), aldolase (160 kDa), catalase (240 kDa), and human H-ferritin (500 kDa)) generated similar AuNPs-protein absorption spectra in a concentration-dependent manner in the range of 1-15 nM. Upon the addition of a protein, the UV-visible spectra of AuNPs-protein conjugates shifted from 524 nm for the AuNps alone to longer wavelength (600-750 nm) due to the presence of one of these proteins. This bathochromic shift is accompanied by a color change from a cherry red, to dark purple, and then light grey or colorless if excess protein has been added, indicating the formation of AuNPs-protein conjugates followed by protein-induced aggregation of the AuNPs. High-resolution transmission electron microscopy images revealed uniformly distributed spherical nanoparticles with an average size of 27.5 ± 15.2 nm, increasing in size to 39.6 ± 12.9 nm upon the addition of a protein, indicating the formation of AuNPs-protein conjugates in solution. A general mechanism for the protein-induced aggregation of our AuNPs is proposed. The consistent behavior observed with the nine proteins tested in our study suggests that our assay can be universally applied for the quantification of pure proteins in a solution, regardless of size, shape, or molecular weight.

Protein-nanoparticle co-assembly supraparticles for drug delivery: Ultrahigh drug loading and colloidal stability, and instant and complete lysosomal drug release

Two frequent problems hindering clinical translation of nanomedicine are low drug loading and low colloidal stability. Previous efforts to achieve ultrahigh drug loading (>30 %) introduce new hurdles, including lower colloidal stability and others, for clinical translation. Herein, we report a new class of drug nano-carriers based on our recent finding in protein-nanoparticle co-assembly supraparticle (PNCAS), with both ultrahigh drug loading (58 % for doxorubicin, i.e., DOX) and ultrahigh colloidal stability (no significant change in hydrodynamic size after one year). We further show that our PNCAS-based drug nano-carrier possesses a built-in environment-responsive drug release feature: once in lysosomes, the loaded drug molecules are released instantly (<1 min) and completely (∼100 %). Our PNCAS-based drug delivery system is spontaneously formed by simple mixing of hydrophobic nanoparticles, albumin and drugs. Several issues related to industrial production are studied. The ultrahigh drug loading and stability of DOX-loaded PNCAS enabled the delivery of an exceptionally high dose of DOX into a mouse model of breast cancer, yielding high efficacy and no observed toxicity. With further developments, our PNCAS-based delivery systems could serve as a platform technology to meet the multiple requirements of clinical translation of nanomedicines.

Real-Time Optical Tracking of Protein Corona Formation on Single Nanoparticles in Serum

The formation of a protein corona, where proteins spontaneously adhere to the surface of nanomaterials in biological environments, leads to changes in their physicochemical properties and subsequently affects their intended biomedical functionalities. Most current methods to study protein corona formation are ensemble-averaging and either require fluorescent labeling, washing steps, or are only applicable to specific types of particles. Here we introduce real-time all-optical nanoparticle analysis by scattering microscopy (RONAS) to track the formation of protein corona in full serum, at the single-particle level, without any labeling. RONAS uses optical scattering microscopy and enables real-time and in situ tracking of protein adsorption on metallic and dielectric nanoparticles with different geometries directly in blood serum. We analyzed the adsorbed protein mass, the affinity, and the kinetics of the protein adsorption at the single particle level. While there is a high degree of heterogeneity from particle to particle, the predominant factor in protein adsorption is surface chemistry rather than the underlying nanoparticle material or size. RONAS offers an in-depth understanding of the mechanisms related to protein coronas and, thus, enables the development of strategies to engineer efficient bionanomaterials.

Carbocyanine-Based Optical Sensor Array for the Discrimination of Proteins and Rennet Samples Using Hypochlorite Oxidation

Optical sensor arrays are widely used in obtaining fingerprints of samples, allowing for solutions of recognition and identification problems. An approach to extending the functionality of the sensor arrays is using a kinetic factor by conducting indicator reactions that proceed at measurable rates. In this study, we propose a method for the discrimination of proteins based on their oxidation by sodium hypochlorite with the formation of the products, which, in turn, feature oxidation properties. As reducing agents to visualize these products, carbocyanine dyes IR-783 and Cy5.5-COOH are added to the reaction mixture at pH 5.3, and different spectral characteristics are registered every several minutes (absorbance in the visible region and fluorescence under excitation by UV (254 and 365 nm) and red light). The intensities of the photographic images of the 96-well plate are processed by principal component analysis (PCA) and linear discriminant analysis (LDA). Six model proteins (bovine and human serum albumins, γ-globulin, lysozyme, pepsin, and proteinase K) and 10 rennet samples (mixtures of chymosin and pepsin from different manufacturers) are recognized by the proposed method. The method is rapid and simple and uses only commercially available reagents.

From prevention to diagnosis and treatment: Biomedical applications of metal nanoparticle-hydrogel composites

Recent advances in biomaterials integrate metal nanoparticles with hydrogels to generate composite materials that exhibit new or improved properties. By precisely controlling the composition, arrangement and interactions of their constituents, these hybrid materials facilitate biomedical applications through myriad approaches. In this work we seek to highlight three popular frameworks for designing metal nanoparticle-hydrogel hybrid materials for biomedical applications. In the first approach, the properties of metal nanoparticles are incorporated into a hydrogel matrix such that the composite is selectively responsive to stimuli such as light and magnetic flux, enabling precisely activated therapeutics and self-healing biomaterials. The second approach mediates the dynamic reorganization of metal nanoparticles based on environment-directed changes in hydrogel structure, leading to chemosensing, microbial and viral detection, and drug-delivery capabilities. In the third approach, the hydrogel matrix spatially arranges metal nanoparticles to produce metamaterials or passively enhance nanoparticle properties to generate improved substrates for biomedical applications including tissue engineering and wound healing. This article reviews the construction, properties and biomedical applications of metal nanoparticle-hydrogel composites, with a focus on how they help to prevent, diagnose and treat diseases. Discussion includes how the composites lead to new or improved properties, how current biomedical research leverages these properties and the emerging directions in this growing field.

A high-throughput plasmonic tongue using an aggregation assay and nonspecific interactions: classification of taste profiles in maple syrup

A simple colorimetric test detects off-flavour profiles of maple syrups in minutes, which are detectable by the naked eye. As flavour profiles are due to complex mixtures of molecules, the test uses nonspecific interactions for analysing the aggregation and color change of Au nanoparticles (AuNPs) induced by the different organic molecules contained in off-flavour maple syrup. The test was optimal with 13 nm citrate-capped AuNPs reacting 1 : 1 with pure maple syrup diluted 10 times. Under these conditions, normal flavour maple syrups did not react and the solution remained red, while off-flavoured maple syrups aggregated the AuNPs and the solution turned blue. Different classes of molecules were then tested to evaluate the types of compounds typically found in maple syrups reacting in the test, showing that sulfur- and amine-containing amino acids and aromatic amines caused aggregation of the AuNPs. The test was validated with 1818 maple syrup samples from the 2018 harvest in Quebec and 98% of the off-flavoured maple syrups were positively identified against the standard taste test. Preliminary tests were performed on site in maple sugar shacks to validate the applicability of the test on the production site.

Spontaneous and instant formation of highly stable protein-nanoparticle supraparticle co-assemblies driven by hydrophobic interaction

Recently, supraparticle protein-nanoparticle co-assemblies (or 'supraparticle co-assemblies' for short) have attracted considerable interest due to their fundamental and technological value. However, it remains challenging to form supraparticle co-assemblies with high stability. Here, we show that using hydrophobic interaction, instead of the previously used electrostatic and van der Waals interactions, as the primary driving force can lead to instant formation of exceptionally stable supraparticle co-assemblies with minimal external energy input. Our formation method of supraparticle co-assemblies simply involves mixing globular proteins (e.g., bovine serum albumin) with hydrophobic nanoparticles (e.g., hydrophobic magnetic nanoparticles and hydrophobic quantum dots) without significant energy input (e.g., sonication or stirring). Upon mixing of hydrophobic nanoparticles and proteins, the formation of supraparticle co-assemblies only takes <1 minute. Further incubation of the mixture for several hours results in a gradual increase of the size uniformity of supraparticle co-assemblies. The formed supraparticle co-assemblies have been colloidally stable for 6 months and counting, and can withstand harsh environments such as basic and acidic pH, high temperature, high dilution, and serum. Co-encapsulation of different sizes/types of nanoparticles is found to be feasible and the co-encapsulation number ratio of different nanoparticles is well-controlled by the feeding ratio. Proof-of-concept studies show the potential of the supraparticle co-assemblies for biological imaging, delivery, and modulation. The combination of very rapid formation, minimal energy consumption, highly stable products, and inexpensive raw materials of this hydrophobic interaction-driven process meets many of the main goals of 'ideal' nano-manufacturing. Thus, this process could serve as the foundation of ideal manufacturing of supraparticle co-assemblies.

Producing protein-nanoparticle co-assembly supraparticles by the interfacial instability process

Originally discovered in fundamental research of nanomaterial-biomolecule interactions, protein-nanoparticle co-assembly supraparticles (PNCAS) have become an emerging class of nanomaterials with various biological applications. We apply the interfacial instability process, which was originally reported for forming nanoparticles-encapsulated polymeric micelles, to produce PNCAS. By doing so hydrophobic nanoparticles, which are often the product formed from the upstream nanoparticle synthesis step, can be directly used as the raw materials of the production process of PNCAS. On the other hand, we take advantage of the structural features of protein molecules, in comparison with amphiphilic block copolymers, to mitigate two common problems encountered in the original interfacial instability-mediated nanoparticle encapsulation process, namely (1) poor encapsulation number control and (2) inconvenience and high cost to vary the assembly size. Additionally, we achieve semi-continuous and scalable production of PNCAS by combining the electrospray process and the interfacial instability process. We also conduct proof-of-concept studies of biological applications of the PNCAS products.

Quantitative micro-Raman analysis of micro-particles in drug delivery

Polymeric micro and nanoconstructs are emerging as promising delivery systems for therapeutics and contrast agents in microcirculation. Excellent assets associated with polymeric particulates of tunable shape, size, mechanical and chemical properties may improve the efficiency of delivery and represent the basis of personalized medicine and treatment. Nevertheless, lack of effective techniques of analysis may limit their use in biomedicine and bioengineering. In this paper, we demonstrated Raman Spectroscopy for quantitative characterization of poly lactic-co-glycolic acid (PLGA) micro-plate drug delivery systems. To do so, we (i) acquired bi-dimensional Raman maps of PLGA micro-plates loaded with curcumin at various times of release over multiple particles. We (ii) realized an exploratory analysis of data using the principal component analysis (PCA) technique to find hidden patterns in the data and reduce the dimensionality of the system. Then, we (iii) used an innovative univariate method of analysis of the reduced system to derive quantitative drug release profiles. High performance liquid chromatography (HPLC), the consolidated method of analysis of macro-sized systems, was used for comparison. We found that our system is as efficient as HPLC but, differently from HPLC, it enables quantitative analysis of systems at the single particle level.

Low-Fouling Characteristics of Ultrathin Zwitterionic Cysteine SAMs

Surface fouling remains an exigent issue for many biological implants. Unwanted solutes adsorb to reduce device efficiency and hasten degradation while increasing the risks of microbial colonization and adverse inflammatory response. To address unwanted fouling in modern implants in vivo, surface modification with antifouling polymers has become indispensable. Recently, zwitterionic self-assembled monolayers, which contain two or more charged functional groups but are electrostatically neutral and form highly hydrated surfaces, have been the focus of many antifouling coatings. Reports using various compositions of zwitterionic polymer brushes have demonstrated ultralow fouling in the ng/cm² range. These coatings, however, are thick and can hinder the target application of biological devices. Here, we report an ultrathin (8.52 Å) antifouling self-assembled monolayer composed of cysteine that is amenable to facile fabrication. The antifouling characteristics of the zwitterionic surfaces were evaluated against bovine serum albumin, fibrinogen, and human blood in real time using quartz crystal microbalance and surface plasmon resonance imaging. Compared to untreated gold surfaces, the ultrathin cysteine coating reduced the adsorption of bovine serum albumin by 95% (43 ng/cm² adsorbed) after 3 h and 90% reduction after 24 h. Similarly, the cysteine self-assembled monolayer reduced the adsorption of fibrinogen as well as human blood by >90%. The surfaces were further characterized using scanning electron microscopy: protein-enhanced adsorption and cellular adsorption in human blood was found on untreated surfaces but not on the cysteine SAM-protected surfaces. These findings suggest that surfaces can be functionalized with an ultrathin layer of cysteine to resist the adsorption of key proteins, with performance comparable to zwitterionic polymer brushes. As such, cysteine surface coatings are a promising methodology to improve the long-term utility of biological devices.

Techniques for the experimental investigation of the protein corona

Due to its enormous relevance the corona formation of adsorbed proteins around nanoparticles is widely investigated. A comparison of different experimental techniques is given. Direct measurements of proteins, such as typically performed with mass spectrometry, will be compared with indirect analysis, in which instead information about the protein corona is gathered from changes in the properties of the nanoparticles. The type of measurement determines also whether before analysis purification from unbound excess proteins is necessary, which may change the equilibrium, or if measurements can be performed in situ without required purification. Pros and contras of the different methods will be discussed.