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It has recently been shown that surface plasmon microscopy (SPM) allows single nanoparticles (NPs) on sensor surfaces to be detected and analyzed. The authors have applied this technique to study the adsorption of single metallic and plastic NPs. Binding of gold NPs (40, 60 and 100 nm in size) and of 100 nm polystyrene NPs to gold surfaces modified by differently ω-functionalized alkyl thiols was studied first. Self-assembled monolayers (SAM) with varying terminal functions including amino, carboxy, oligo(ethylene glycol), methyl, or trimethylammonium groups were deposited on gold films to form surfaces possessing different charge and hydrophobicity. The affinity of NPs to these surfaces depends strongly on the type of coating. SAMs terminated with trimethylammonium groups and carboxy group display highly different affinity and therefore were preferred when creating patterned charged surfaces. Citrate-stabilized gold NPs and sulfate-terminated polystyrene NPs were used as negatively charged NPs, while branched polyethylenimine-coated silver NPs were used as positively charged NPs. It is shown that the charged patterned areas on the gold films are capable of selectively adsorbing oppositely charged NPs that can be detected and analyzed with an ~1 ng⋅mL−1 detection limit.
A new approach for self-referencing in SPR biosensors is reported. The method is technologically simple and applicable for a wide range of existing SPR instrumentation with Kretschmann configuration. It is based on the micropatterning of the sensor area with sensing and referencing areas whose shape and distribution can be chosen arbitrarily and their characteristic sizes are larger than the plasmons propagation length. Provided that roughly a half of the area is used as the sensing area while its optical thickness is different from that of the referencing area, an integral measurement of the intensity of the reflected light over such a patterned surface near the summary resonance conditions exhibits self-referencing properties. An over ten-fold suppression of the effect caused by the variation of the bulk refractive index was observed.
An ultrasensitive analytical method for direct detection of single nanoparticles in complex environment is described. The method relies on the wide-field surface plasmon microscopy (SPM). The suppression of matrix effects is achieved by image analysis based on the template matching. First, characteristic SPM images of nanoparticles are collected in aqueous suspensions. Then the detection of nanoparticles in complex environment is performed using template matching.
Quantification and characterization of nanoparticles size was demonstrated at subppb level (∼ 100 pg/mL) in such complex media as wines, fruit juices, or cosmetic formulation. Visualization of the nanoparticles is performed in real time. The method does not require any sample pretreatment. If the minimally acceptable adsorption rate is defined as one nanoparticle to the whole sensor surface per few seconds, the working range of the method is ∼ 10 6 to 10 10
nanoparticles per mL.
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.
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.
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.