Refine
Document Type
Keywords
Institute
Development of nanotechnology and corresponding industries during the last decade resulted in a new challenge for analytical science. This includes an ultrasensitive detection and characterization of nanoparticles of different origin and other nanomaterials in various media, including so complex ones as food, biological or environmental samples. The goal of this review is a systematic analysis of possible approaches and description of physical principles behind these methods. The main attention is paid to optical methods which are considered by authors to be mostly effective for the formulated task. Different approaches for detection and analysis of nanoparticles in a volume as well as of those adsorbed on a surface are discussed. While the technologies based on direct analysis of nanoparticle suspensions belong to the established approaches whose development potential has been in large extent exhausted, the novel technologies based on the surface sensing of adsorbed nanoparticles demonstrate intensive development. Therefore, the final part of the review is focused on the wide-field surface plasmon resonance microscopy. It allows one an ultrasensitive detection and characterization of individual nanoparticles of different origin in complex media and provides numerous possibilities for subsequent chemical identification of the detected particles using a hyphenation with other analytical technologies.
An analysis of early stage of electrochemical nucleation is crucial in order to understand the mechanism of this process and for electrochemical synthesis of new materials. We show here an application of the wide field surface plasmon microscopy (WF-SPRM) for this purpose. It allows us in-situ monitoring of the growth of nuclei in the range from ~20 till over 1000 nm. The system registers the moment and the place of the formation of each individual nucleus for the total number of the tracked nuclei up to ~10,000 per 1 mm2. The results demonstrate that the integral information obtained from electrochemical measurements can be extracted quantitatively from optical measurements while optical data provide also information on the size of each individual nucleus, individual nucleation time, localization and growth kinetics, and allows one to distinguish the rate limiting stage for each individual nucleus. In this work WF-SPRM was applied for investigation of electrochemical deposition of copper on gold, but this technique can be extended easily to other materials or other nucleation types.
Despite the history of application of surface plasmon resonance (SPR) for chemo- and biosensing being over 30 years long, the development of this technique is still in progress.
This review is focused on the technological aspects of further improvement of analytical performance of SPR transducers based on Kretschmann configuration. We describe basic measurement configurations, their improvements and optimizations, and their drawbacks and limitations. An importance of referencing in SPR sensors is highlighted. The referencing approaches are classified into the following domains: (1) macroscopic spatially separated referencing, (2) self-referencing based on micro-patterning, (3) in-place referencing, (4) spatiotemporal referencing, and (5) electrochemically assisted referencing. The underlying principles of these approaches, examples of their implementation, and resulting improvements of sensor performance are described. Finally, an analysis of SPR data and an extraction of affinity properties are discussed.
An approach for visualization of patterned monomolecular layers in surface plasmon microscopy (SPM) is suggested. The development of hidden image in SPM is achieved by referencing of images obtained in the presence of electrolytes with a high molar refraction of either anions or cations. A formation of diffuse layer near the charged surface areas leads to the redistribution of ions. The ratio of SPM images allows one to visualize this redistribution and to distinguish surface areas with different properties. The approach is unobtrusive and robust; it can be used with most SPR imaging instruments.
Surface plasmon resonance, being widely used in bioanalytics and biotechnology, is influenced by the electrical potential of the resonant gold layer. To evaluate the mechanism of this effect, we have studied it in solutions of various inorganic electrolytes. The magnitude of the effect decreases according to the series: KBr>KCl>KF>NaClO4. The data were treated by using different models of the interface. A quantitative description was obtained for the model, which takes into account the local dielectric function of gold being affected by the free electron charge, diffuse ionic layer near the gold/water interface, and specific adsorption of halides to the gold surface with partial charge transfer. Taking into account that most biological experiments are performed in chloride-containing solutions, detailed analysis of the model at these conditions was performed. The results indicate that the chloride adsorption is the main mechanism for the influence of potential on the surface plasmon resonance. The dependencies of surface concentration and residual charge of chloride on the applied potential were determined.
In-situ detection and characterization of nanoparticles in biological media as well as in food or other complex samples is still a big challenge for existing analytical methods. Here we describe a label-free and cost-effective analytical method for detection of nanoparticles in the concentration range 106 -1010 NPs/ml. The proposed method is based on the surface plasmon resonance microscopy (SPRM) with a large field of view (~1.3mm2 ). It is able to detect and count adsorbing nanoparticles individually, totally up to the hundreds of thousands of NPs on the sensor surface. At constant diffusion conditions the detection rate is proportional to the number concentration of NPs, this provides an approach to determine the NPs concentration. The adsorption of nanoparticle can be manipulated by the surface functionalization, pH and electrolyte concentration of suspensions. Images of detected nanoparticles can be quantified in order to characterize them individually. The image intensity grows quasi-linearly with nanoparticle size for the given material. However, the size and material of nanoparticle cannot be resolved directly from the image. For determination of chemical composition, SPRM can be assisted by electrochemical analysis. In this case, the gold sensor surface is used both as a resonant media for plasmon microscopy and as a working electrode. Under potential sweep, the adsorbed NPs can be subjected to electrochemical dissolution, which is detected optically. The potential of this conversion characterizes the material of NPs.
Detection of nano- and micro-particles is an important task for chemical analytics, food industry, biotechnology, environmental monitoring and many other fields of science and industry. For this purpose, a method based on the detection and analysis of minute signals in surface plasmon resonance images due to adsorption of single nanopartciles was developed. This new technology allows one a real-time detection of interaction of single nano- and micro-particles with sensor surface. Adsorption of each nanoparticle leads to characteristic diffraction image whose intensity depends on the size and chemical composition of the particle. The adsorption rate characterizes volume concentration of nano- and micro-particles. Large monitored surface area of sensor enables a high dynamic range of counting and to a correspondingly high dynamic range in concentration scale. Depending on the type of particles and experimental conditions, the detection limit for aqueous samples can be below 1000 particles per microliter. For application of method in complex media, nanoparticle images are discriminated from image perturbations due to matrix components. First, the characteristic SPRM images of nanoparticles (templates) are collected in aqueous suspensions or spiked real samples. Then, the detection of nanoparticles in complex media using template matching is performed. The detection of various NPs in consumer products like cosmetics, mineral water, juices, and wines was shown at sub-ppb level. The method can be applied for ultrasensitive detection and analysis of nano- and micro-particles of biological (bacteria, viruses, endosomes), biotechnological (liposomes, protein nanoparticles for drug delivery) or technical origin.
Detection of nano- and microparticles is an important task for chemical analytics, medical diagnostics, food industry, biotechnology, environmental monitoring and many other fields of science and industry. For this purpose, a method based on the detection and analysis of minute signals of surface plasmon resonance images due to adsorption of single particles was developed.
The new technology allows one a real-time detection of interaction of single nano- and microparticles of different origin with sensor surface. Adsorption of each nanoparticle leads to a characteristic diffraction image whose intensity depends on the size and chemical composition of the particle. The number of the nanoparticle - surface binding events per time and surface area characterizes volume concentration. A large monitored surface area of the sensor surface allows one to detect many hundreds events in each frame or totally up to a million particles on the sensor surface, this leads to a very high dynamic range of counting and to a correspondingly high dynamic range in the concentration scale. Depending on the type of particles and experimental conditions, the detection limit for aqueous samples can be below 1000 nanoparticles per microliter. Stable analysis of
nanoparticles in very complex environment (fruit juices, wines, cosmetic formulations) was demonstrated.
For determination of chemical composition of single nanoparticles separately, the wide field surface plasmon microscopy can be used as a tandem technique. For example, for analysis of technical nanoparticles it can be assisted by electrochemical analysis. In this case, the gold sensor surface is used both for plasmon microscopy and as a working electrode of electrochemical cell. Applying a linear potential sweep to this electrode, adsorbed nanoparticles can be subjected to an electrochemical conversion leading to the change of their refractive index; the value of electrical potential of this conversion characterizes material of the particular nanoparticle. Notably, such analysis is performed simultaneously but independently for each adsorbed particle.
The method of wide filed surface plasmon microscopy can be applied for ultrasensitive detection and analysis of nano- and microparticles of biological (bacteria, viruses, exosomes), biotechnological, (liposomes, protein nanoparticles for drug delivery) or technical (metallic, oxides, plastic, etc.) origin.