Ordered Surface Structuring of Spherical Colloids with Binary Nanoparticle Superlattices.

Surface-patterning colloidal matter in the sub-10 nm regime generates exceptional functionality in biology and photonic and electronic materials. Techniques of artificially generating functional patterns in the small nanoscale advanced in a fascinating manner in the last several years. However, they remain often restricted to planar and noncolloidal substrates. Patterning colloidal matter in solution via bottom-up assembly of smaller subunits on larger core particles is highly challenging because it is necessary to force the subunits onto randomly moving objects. Consequently, the non-equilibrium conditions present during nanoparticle self-assembly are difficult to control to eventually achieve the desired material structures. Here, we describe the formation of surface patterns with intrinsic periodic repeats of 8.9 ± 0.9 nm and less on hard, amorphous colloidal core particles by assembling binary nanoparticle superlattices on the curved particle surface. The colloidal environment is preserved during the entire bottom-up crystallization of variable building blocks (here, monodispersed 5 nm Au and 2.4 nm Pd nanoparticles (NPs) and 230 nm SiO2 core particles) into AB13-like, binary, and isotropic superlattice domains on the amorphous cores. The three-dimensional, bottom-up assembly technique is a new tool for patterning colloidal matter in the sub-10 nm surface regime for gaining access to multicomponent metamaterials for bionanoscience, photonics, and electronics.

Locating Reactive Groups on Nanomaterials with Gold Nanoclusters: Toward a Surface Reactive Site Map.

Nanoparticles (NPs) are often functionalized with reactive groups such as amines and thiols for the subsequent conjugation of further molecules, e.g., stabilizing polymers, drugs, and proteins for targeting cells or specific diseases. In addition to the quantitative estimation of the reactive conjugation sites, their molecular positioning and nanoscale arrangement on single nanoparticles become more and more important for the tailored engineering and design of functional nanomaterials. Here, we use maleimide or sulfo-succinimidyl ester-modified 1.4 nm gold nanoclusters (AuNCs) to specifically label reactive thiol and amine groups with sub-2-nm precision on metal oxide and polymeric nanostructures. We confirm the binding of AuNCs by measuring and modeling sedimentation properties using analytical centrifugation, imaging their surface distribution and surface distances by transmission electron microscopy (TEM), and comparing the results to ensemble measurements of numbers of reactive surface groups obtained by common photometric assays. We map thiol and amine groups introduced on silica NPs (SiNPs), titania stars (Ti), silica inverse opals (SiOps), and polystyrene NPs (PS NPs). We show that the method is suitable for mapping local, clustered inhomogeneities of the reactive sites on single SiNPs introduced by masking certain areas during surface functionalization. Mapping precise positions of reactive surface groups is essential to the design and tailored ligation of multifunctional nanomaterials.

Charge generation by passive plant leaf motion at low wind speeds: design and collective behavior of plant-hybrid energy harvesters.

Energy harvesting techniques can exploit even subtle passive motion like that of plant leaves in wind as a consequence of contact electrification of the leaf surface. The effect is strongly enhanced by artificial materials installed as 'artificial leaves' on the natural leaves creating a recurring mechanical contact and separation. However, this requires a controlled mechanical interaction between the biological and the artificial component during the complex wind motion. Here, we build and test four artificial leaf designs with varying flexibility and degrees of freedom across the blade operating onNerium oleanderplants. We evaluate the apparent contact area (up to 10 cm2per leaf), the leaves' motion, together with the generated voltage, current and charge in low wind speeds of up to 3.3 m s-1and less. Single artificial leaves produced over 75 V and 1µA current peaks. Softer artificial leaves increase the contact area accessible for energy conversion, but a balance between softer and stiffer elements in the artificial blade is optimal to increase the frequency of contact-separation motion (here up to 10 Hz) for energy conversion also below 3.3 m s-1. Moreover, we tested how multiple leaves operating collectively during continuous wind energy harvesting over several days achieve a root mean square power of ∼6µW and are capable to transfer ∼80µC every 30-40 min to power a wireless temperature and humidity sensor autonomously and recurrently. The results experimentally reveal design strategies for energy harvesters providing autonomous micro power sources in plant ecosystems for example for sensing in precision agriculture and remote environmental monitoring.

Adsorption and orientation of the physiological extracellular peptide glutathione disulfide on surface functionalized colloidal alumina particles.

Understanding the interrelation between surface chemistry of colloidal particles and surface adsorption of biomolecules is a crucial prerequisite for the design of materials for biotechnological and nanomedical applications. Here, we elucidate how tailoring the surface chemistry of colloidal alumina particles (d50 = 180 nm) with amino (-NH2), carboxylate (-COOH), phosphate (-PO3H2) or sulfonate (-SO3H) groups affects adsorption and orientation of the model peptide glutathione disulfide (GSSG). GSSG adsorbed on native, -NH2-functionalized, and -SO3H-functionalized alumina but not on -COOH- and -PO3H2-functionalized particles. When adsorption occurred, the process was rapid (≤5 min), reversible by application of salts, and followed a Langmuir adsorption isotherm dependent on the particle surface functionalization and ζ potential. The orientation of particle bound GSSG was assessed by the release of glutathione after reducing the GSSG disulfide bond and by ζ potential measurements. GSSG is likely to bind via the carboxylate groups of one of its two glutathionyl (GS) moieties onto native and -NH2-modified alumina, whereas GSSG is suggested to bind to -SO3H-modified alumina via the primary amino groups of both GS moieties. Thus, GSSG adsorption and orientation can be tailored by varying the molecular composition of the particle surface, demonstrating a step toward guiding interactions of biomolecules with colloidal particles.

Controlling mixed-protein adsorption layers on colloidal alumina particles by tailoring carboxyl and hydroxyl surface group densities.

We show that different ratios of bovine serum albumin (BSA) and lysozyme (LSZ) can be achieved in a mixed protein adsorption layer by tailoring the amounts of carboxyl (-COOH) and aluminum hydroxyl (AlOH) groups on colloidal alumina particles (d50 ≈ 180 nm). The particles are surface-functionalized with -COOH groups, and the resultant surface chemistry, including the remaining AlOH groups, is characterized and quantified using elemental analysis, ζ potential measurements, acid-base titration, IR spectroscopy, electron microscopy, nitrogen adsorption, and dynamic light scattering. BSA and LSZ are subsequently added to the particle suspensions, and protein adsorption is monitored by in situ ζ potential measurements while being quantified by UV spectroscopy and gel electrophoresis. A comparison of single-component and sequential protein adsorption reveals that BSA and LSZ have specific adsorption sites: BSA adsorbs primarily via AlOH groups, whereas LSZ adsorbs only via -COOH groups (1-2 -COOH groups on the particle surface is enough to bind one LSZ molecule). Tailoring such groups on the particle surface allows control of the composition of a mixed BSA and LSZ adsorption layer. The results provide further insight into how particle surface chemistry affects the composition of protein adsorption layers on colloidal particles and is valuable for the design of such particles for biotechnological and biomedical applications.

Virus removal in ceramic depth filters based on diatomaceous earth.

Ceramic filter candles, based on the natural material diatomaceous earth, are widely used to purify water at the point-of-use. Although such depth filters are known to improve drinking water quality by removing human pathogenic protozoa and bacteria, their removal regarding viruses has rarely been investigated. These filters have relatively large pore diameters compared to the physical dimension of viruses. However, viruses may be retained by adsorption mechanisms due to intermolecular and surface forces. Here, we use three types of bacteriophages to investigate their removal during filtration and batch experiments conducted at different pH values and ionic strengths. Theoretical models based on DLVO-theory are applied in order to verify experimental results and assess surface forces involved in the adsorptive process. This was done by calculation of interaction energies between the filter surface and the viruses. For two small spherically shaped viruses (MS2 and PhiX174), these filters showed no significant removal. In the case of phage PhiX174, where attractive interactions were expected, due to electrostatic attraction of oppositely charged surfaces, only little adsorption was reported in the presence of divalent ions. Thus, we postulate the existence of an additional repulsive force between PhiX174 and the filter surface. It is hypothesized that such an additional energy barrier originates from either the phage's specific knobs that protrude from the viral capsid, enabling steric interactions, or hydration forces between the two hydrophilic interfaces of virus and filter. However, a larger-sized, tailed bacteriophage of the family Siphoviridae was removed by log 2 to 3, which is explained by postulating hydrophobic interactions.

Wind dynamics and leaf motion: Approaching the design of high-tech devices for energy harvesting for operation on plant leaves.

High-tech sensors, energy harvesters, and robots are increasingly being developed for operation on plant leaves. This introduces an extra load which the leaf must withstand, often under further dynamic forces like wind. Here, we took the example of mechanical energy harvesters that consist of flat artificial "leaves" fixed on the petioles of N. oleander, converting wind energy into electricity. We developed a combined experimental and computational approach to describe the static and dynamic mechanics of the natural and artificial leaves individually and join them together in the typical energy harvesting configuration. The model, in which the leaves are torsional springs with flexible petioles and rigid lamina deforming under the effect of gravity and wind, enables us to design the artificial device in terms of weight, flexibility, and dimensions based on the mechanical properties of the plant leaf. Moreover, it predicts the dynamic motions of the leaf-artificial leaf combination, causing the mechanical-to-electrical energy conversion at a given wind speed. The computational results were validated in dynamic experiments measuring the electrical output of the plant-hybrid energy harvester. Our approach enables us to design the artificial structure for damage-safe operation on leaves (avoiding overloading caused by the interaction between leaves and/or by the wind) and suggests how to improve the combined leaf oscillations affecting the energy harvesting performance. We furthermore discuss how the mathematical model could be extended in future works. In summary, this is a first approach to improve the adaptation of artificial devices to plants, advance their performance, and to counteract damage by mathematical modelling in the device design phase.

A perspective on plant robotics: from bioinspiration to hybrid systems.

As miscellaneous as the Plant Kingdom is, correspondingly diverse are the opportunities for taking inspiration from plants for innovations in science and engineering. Especially in robotics, properties like growth, adaptation to environments, ingenious materials, sustainability, and energy-effectiveness of plants provide an extremely rich source of inspiration to develop new technologies-and many of them are still in the beginning of being discovered. In the last decade, researchers have begun to reproduce complex plant functions leading to functionality that goes far beyond conventional robotics and this includes sustainability, resource saving, and eco-friendliness. This perspective drawn by specialists in different related disciplines provides a snapshot from the last decade of research in the field and draws conclusions on the current challenges, unanswered questions on plant functions, plant-inspired robots, bioinspired materials, and plant-hybrid systems looking ahead to the future of these research fields.

Biohybrid generators based on living plants and artificial leaves: influence of leaf motion and real wind outdoor energy harvesting.

Plants translate wind energy into leaf fluttering and branch motion by reversible tissue deformation. Simultaneously, the outermost structure of the plant, i.e. the dielectric cuticula, and the inner ion-conductive tissue can be used to convert mechanical vibration energy, such as that produced during fluttering in the wind, into electricity by surface contact electrification and electrostatic induction. Constraining a tailored artificial leaf to a plant leaf can enhance oscillations and transient mechanical contacts and thereby increase the electricity outcome. We have studied the effects of wind-induced mechanical interactions between the leaf of a plant (Rhododendron) and a flexible silicone elastomer-based artificial leaf fixed at the petiole on power output and whether performance can be further tuned by altering the vibrational behavior of the artificial leaf. The latter is achieved by modifying a concentrated mass at the tip of the artificial leaf and observing plant-generated current and voltage signals under air flow. In this configuration, the plant-hybrid wind-energy converters can directly power light-emitting diodes and a temperature sensor. Detailed output analysis has revealed that, under all conditions, an increase in wind speed leads to nearly linearly increased voltages and currents. Accordingly, the cumulative sum energy reaches its highest values at the highest wind speed and resulting oscillations of the plant-artificial leaf system. The mass at the tip can, in most cases, be used to increase the voltage amplitude and frequency. Nevertheless, this behavior was found to depend on the individual configuration of the system, such as the leaf morphology. Analysis of these factors under controlled conditions is crucial for optimizing systems meant to operate in unstructured outdoor scenarios. We have established, in a first approach, that the artificial leaf-plant hybrid generator is capable of autonomously generating electricity outdoors under real outdoor wind conditions, even at a low average wind speed of only 1.9 m s-1.

Remotely Light-Powered Soft Fluidic Actuators Based on Plasmonic-Driven Phase Transitions in Elastic Constraint.

Materials capable of actuation through remote stimuli are crucial for untethering soft robotic systems from hardware for powering and control. Fluidic actuation is one of the most applied and versatile actuation strategies in soft robotics. Here, the first macroscale soft fluidic actuator is derived that operates remotely powered and controlled by light through a plasmonically induced phase transition in an elastomeric constraint. A multiphase assembly of a liquid layer of concentrated gold nanoparticles in a silicone or styrene-ethylene-butylene-styrene elastic pocket forms the actuator. Upon laser excitation, the nanoparticles convert light of specific wavelength into heat and initiate a liquid-to-gas phase transition. The related pressure increase inflates the elastomers in response to laser wavelength, intensity, direction, and on-off pulses. During laser-off periods, heating halts and condensation of the gas phase renders the actuation reversible. The versatile multiphase materials actuate-like soft "steam engines"-a variety of soft robotic structures (soft valve, pnue-net structure, crawling robot, pump) and are capable of operating in different environments (air, water, biological tissue) in a single configuration. Tailored toward the near-infrared window of biological tissue, the structures actuate also through animal tissue for potential medical soft robotic applications.

Labeling the Structural Integrity of Nanoparticles for Advanced In Situ Tracking in Bionanotechnology.

Observing structural integrity of nanoparticles is essential in bionanotechnology but not always straightforward to measure in situ and in real-time. Fluorescent labels used for tracking intrinsically nonfluorescent nanomaterials generally do not allow simultaneous observation of integrity. Consequently, structural changes like degradation and disassembly cannot easily be followed in situ using fluorescence signals. We show that thioflavin T (ThT), a fluorophore and molecular rotor known to tag specific fibril structures in amyloids, can "label" the structural integrity of widely used and intrinsically nonfluorescent, silica nanoparticles (SiNPs). Entrapment of ThT in SiNPs controls the fluorohphore's relaxation pathway and leads to a red-shifted fluorescence spectrum providing real time information on SiNP integrity. The dynamic change of ThT fluorescence during degradation of doped SiNPs is found much higher than that of common labels fluorescein and rhodamine. Degradation kinetics of core-shell structures recorded by ThT fluorescence and light scattering prove the capability to clearly distinguish structural features during SiNPs degradation and allow obtaining degradation kinetics in vitro, in biological media, in serum, and in cells. The effect is transferable to different types of materials, here shown for ThT incorporated SiNPs with tightly tailorable sizes (9-100 nm), poly(lactic-co-glycolic acid) (PLGA) nanoparticles, poly(9-vinylcarbazole) (PVK) nanoparticles, and iron-doped-SiNPs (FeSiNPs). We thus suggest molecular rotors such as ThT as additional labels to effectively and easily sense nanoparticle structural status in situ and to enhance understanding and development of programmed nanoparticle disassembly in bionanotechnology.

Constructing bifunctional nanoparticles for dual targeting: improved grafting and surface recognition assessment of multiple ligand nanoparticles.

Nanoparticles (NPs) functionalized with two active targeting ligands have been proposed in drug delivery for their promising capability to stimulate different pathways with one object. Due to the multivalency, the construction and analysis of the effective surface of such bifunctional nanoparticles, however, is significantly more complex than for nanoparticles bearing only one ligand. Here, we optimize construction and analysis of bifunctional NPs containing recognizable combinations of human serum albumin (HSA), transferrin (Tf), and epidermal growth factor (EGF) on fluorescent silica NPs grafted via common polyethylene glycol (PEG) linkers as a model system. Combined with an overall protein quantification, a mapping of exposed recognizable sequences using monoclonal antibodies conjugated to gold nanoparticles (AuNPs) or quantum dots (QDs) for enhanced spectroscopic and microscopic detection revealed that active protein sequences can be one to two orders of magnitude lower than overall conjugated proteins while possessing specific cellular recognition. In addition, we found that common conjugation strategies lead to a large excess of non-specifically compared to covalently bound ligands and instabilities that may impact targeting. These can be avoided by certain synthetic conditions presented here for effective exploitation of multivalent surfaces in nanomedicine.

Physicochemical properties and biodegradability of organically functionalized colloidal silica particles in aqueous environment.

Engineered sub-micron particles are being used in many technical applications, leading to an increasing introduction into the aquatic environment. Only a few studies have dealt with the biodegradability of non-functionalized organic particles. In fact the knowledge of organically surface functionalized colloids is nearly non-existent. We have investigated the biodegradability of organically surface functionalized silica (SiO2) particles bearing technically relevant groups such as amino-, carboxyl-, benzyl-, sulfonate-, chloro-, and phosphatoethyl-derivatized alkyls. Essential physicochemical properties including zeta potential, isoelectric point, morphology, surface area, porosity, surface density, and elemental composition of the particles were investigated, followed by biodegradability testing using the Closed Bottle Test (OECD 301D). None of the particles met the biodegradability threshold value of 60%. Only a slight biodegradation was revealed for SiO2-Benzyl (13.7±6.7%) and for SiO2-3-Chlorpropane (10.8±1.5%). For the other particles biodegradability was below the normal background fluctuation of 5%. The results were different of those obtained from structurally similar chemicals not being functionalized on the particle surface and from general rules of structure-biodegradation prediction of organic molecules. Therefore, our results suggest that the attachment of the organic groups heavily reduces their biodegradability, increases their residence time and possibility for adverse effects to environmental species.

Gills are an initial target of zinc oxide nanoparticles in oysters Crassostrea gigas, leading to mitochondrial disruption and oxidative stress.

The increasing industrial use of nanomaterials during the last decades poses a potential threat to the environment and in particular to organisms living in the aquatic environment. In the present study, the toxicity of zinc oxide nanoparticles (ZnONP) was investigated in Pacific oysters Crassostrea gigas. The nanoscale of ZnONP, in vehicle or ultrapure water, was confirmed, presenting an average size ranging from 28 to 88 nm. In seawater, aggregation was detected by TEM and DLS analysis, with an increased average size ranging from 1 to 2 µm. Soluble or nanoparticulated zinc presented similar toxicity, displaying a LC50 (96 h) around 30 mg/L. High zinc dissociation from ZnONP, releasing ionic zinc in seawater, is a potential route for zinc assimilation and ZnONP toxicity. To investigate mechanisms of toxicity, oysters were treated with 4 mg/L ZnONP for 6, 24 or 48 h. ZnONP accumulated in gills (24 and 48 h) and digestive glands (48 h). Ultrastructural analysis of gills revealed electron-dense vesicles near the cell membrane and loss of mitochondrial cristae (6 h). Swollen mitochondria and a more conspicuous loss of mitochondrial cristae were observed after 24 h. Mitochondria with disrupted membranes and an increased number of cytosolic vesicles displaying electron-dense material were observed 48 h post exposure. Digestive gland showed similar changes, but these were delayed relative to gills. ZnONP exposure did not greatly affect thiol homeostasis (reduced and oxidized glutathione) or immunological parameters (phagocytosis, hemocyte viability and activation and total hemocyte count). At 24 h post exposure, decreased (-29%) glutathione reductase (GR) activity was observed in gills, but other biochemical responses were observed only after 48 h of exposure: lower GR activity (-28%) and levels of protein thiols (-21%), increased index of lipid peroxidation (+49%) and GPx activity (+26%). In accordance with ultrastructural changes and zinc load, digestive gland showed delayed biochemical responses. Except for a decreased GR activity (-47%) at 48 h post exposure, the biochemical alterations seen in gills were not present in digestive gland. The results indicate that gills are able to incorporate zinc prior (24 h) to digestive gland (48 h), leading to earlier mitochondrial disruption and oxidative stress. Our data suggest that gills are the initial target of ZnONP and that mitochondria are organelles particularly susceptible to ZnONP in C. gigas.

Controlling protein-particle adsorption by surface tailoring colloidal alumina particles with sulfonate groups.

In this study, we demonstrate the control of protein adsorption by tailoring the sulfonate group density on the surface of colloidal alumina particles. The colloidal alumina (d(50)=179±8nm) is first accurately functionalized with sulfonate groups (SO(3)H) in densities ranging from 0 to 4.7SO(3)H nm(-2). The zeta potential, hydrophilic/hydrophobic properties, particle size, morphology, surface area and elemental composition of the functionalized particles are assessed. The adsorption of three model proteins, bovine serum albumin (BSA), lysozyme (LSZ) and trypsin (TRY), is then investigated at pH 6.9±0.3 and an ionic strength of 3mM. Solution depletion and zeta potential experiments show that BSA, LSZ and TRY adsorption is strongly affected by the SO(3)H surface density rather than by the net zeta potential of the particles. A direct correlation between the SO(3)H surface density, the intrinsic protein amino acid composition and protein adsorption is observed. Thus a continuous adjustment of the protein adsorption amount can be achieved between almost no coverage and a theoretical monolayer by varying the density of SO(3)H groups on the particle surface. These findings enable a deeper understanding of protein-particle interactions and, moreover, support the design and engineering of materials for specific biotechnology, environmental technology or nanomedicine applications.

Functionalized ceramics for biomedical, biotechnological and environmental applications.

Surface functionalization has become of paramount importance and is considered a fundamental tool for the development and design of countless devices and engineered systems for key technological areas in biomedical, biotechnological and environmental applications. In this review, surface functionalization strategies for alumina, zirconia, titania, silica, iron oxide and calcium phosphate are presented and discussed. These materials have become particularly important concerning the aforementioned applications, being not only of great academic, but also of steadily increasing human and commercial, interest. In this review, special emphasis is given to their use as biomaterials, biosensors, biological targets, drug delivery systems, implants, chromatographic supports for biomolecule purification and analysis, and adsorbents for toxic substances and pollutants. The objective of this review is to provide a broad picture of the enormous possibilities offered by surface functionalization and to identify particular challenges regarding surface analysis and characterization.

The role of surface functionalization of colloidal alumina particles on their controlled interactions with viruses.

Materials that interact in a controlled manner with viruses attract increasing interest in biotechnology, medicine, and environmental technology. Here, we show that virus-material interactions can be guided by intrinsic material surface chemistries, introduced by tailored surface functionalizations. For this purpose, colloidal alumina particles are surface functionalized with amino, carboxyl, phosphate, chloropropyl, and sulfonate groups in different surface concentrations and characterized in terms of elemental composition, electrokinetic, hydrophobic properties, and morphology. The interaction of the functionalized particles with hepatitis A virus and phages MS2 and PhiX174 is assessed by virus titer reduction after incubation with particles, activity of viruses conjugated to particles, and imaged by electron microscopy. Type and surface density of particle functional groups control the virus titer reduction between 0 and 99.999% (5 log values). For instance, high sulfonate surface concentrations (4.7 groups/nm(2)) inhibit attractive virus-material interactions and lead to complete virus recovery. Low sulfonate surface concentrations (1.2 groups/nm(2)), native alumina, and chloropropyl-functionalized particles induce strong virus-particle adsorption. The virus conformation and capsid amino acid composition further influence the virus-material interaction. Fundamental interrelations between material properties, virus properties, and the complex virus-material interaction are discussed and a versatile pool of surface functionalization strategies controlling virus-material interactions is presented.

Fluorescence labeling of colloidal core-shell particles with defined isoelectric points for in vitro studies.

In the light of in vitro nanotoxicological studies fluorescence labeling has become standard for particle localization within the cell environment. However, fluorescent labeling is also known to significantly alter the particle surface chemistry and therefore potentially affect the outcome of cell studies. Hence, fluorescent labeling is ideally carried out without changing, for example, the isoelectric point. A simple and straightforward method for obtaining fluorescently labeled spherical metal oxide particles with well-defined isoelectric points and a narrow size distribution is presented in this study. Spherical amorphous silica (SiO2, 161 nm diameter) particles were used as the substrate material and were coated with silica, alumina (Al2O3), titania (TiO2), or zirconia (ZrO2) using sol-gel chemistry. Fluorescent labeling was achieved by directly embedding rhodamine 6G dye in the coating matrix without affecting the isoelectric point of the metal oxide coatings. The coating quality was confirmed by high resolution transmission electron microscopy, energy filtered transmission electron microscopy and electrochemical characterization. The coatings were proven to be stable for at least 240 h under different pH conditions. The well-defined fluorescent particles can be directly used for biomedical investigations, e.g. elucidation of particle-cell interactions in vitro.

Protein adsorption on colloidal alumina particles functionalized with amino, carboxyl, sulfonate and phosphate groups.

Colloidal oxide particles in biomedical or biotechnological applications immediately become coated with proteins of the biological medium, a process which is strongly influenced by the surface characteristics of the particles. Fundamental correlations between surface characteristics and the, so far mainly uncontrollable, protein adsorption are still not clear. In this study the surface of colloidal alumina particles (d(50)=179 ± 8 nm) was systematically adjusted with NH(2), COOH, SO(3)H and PO(3)H(2) functional groups to investigate the influence on the adsorption of the three model proteins, bovine serum albumin (BSA), lysozyme (LSZ) and trypsin (TRY). The surface functionalization is characterized and discussed in detail with regard to the morphology, isoelectric point, zeta potential, hydrophilic/hydrophobic properties, functional group density and stability. Protein-particle interaction was then assessed by evaluating the amount of protein adsorbed and the zeta potentials of protein-particle conjugates. Protein adsorption was found to be influenced by the type of functional group as well as the expected electrostatic forces under the given experimental conditions. The level of protein adsorption might, hence, be specifically controlled by the type of surface functionalization. Possible adsorption modes of BSA, LSZ and TRY on the particles are suggested by considering the spatial surface potential distribution of the proteins calculated from the protein database file. The particles presented provide an excellent prerequisite for further investigation of fundamental particle-protein interactions and the design of functionally graded materials for biomedical and biotechnological applications, e.g. as drug carriers or for protein purification.