Direct protein quantification in complex sample solutions by surface-engineered nanorod probes

Detecting biomarkers from complex sample solutions is the key objective of molecular diagnostics. Being able to do so in a simple approach that does not require laborious sample preparation, sophisticated equipment and trained staff is vital for point-of-care applications. Here, we report on the specific detection of the breast cancer biomarker sHER2 directly from serum and saliva samples by a nanorod-based homogeneous biosensing approach, which is easy to operate as it only requires mixing of the samples with the nanorod probes. By careful nanorod surface engineering and homogeneous assay design, we demonstrate that the formation of a protein corona around the nanoparticles does not limit the applicability of our detection method, but on the contrary enables us to conduct in-situ reference measurements, thus further strengthening the point-of-care applicability of our method. Making use of sandwich assays on top of the nanorods, we obtain a limit of detection of 110 pM and 470 pM in 10-fold diluted spiked saliva and serum samples, respectively. In conclusion, our results open up numerous applications in direct protein biomarker quantification, specifically in point-of-care settings where resources are limited and ease-of-use is of essenceThis research was supported by the European Commission FP7 NAMDIATREAM project (EU NMP4-LA-2010–246479), and the German Research Foundation (DFG grant PA 794/25-1)S

Homogeneous Biosensing Based on Magnetic Particle Labels

The growing availability of biomarker panels for molecular diagnostics is leading to an increasing need for fast and sensitive biosensing technologies that are applicable to point-of-care testing. In that regard, homogeneous measurement principles are especially relevant as they usually do not require extensive sample preparation procedures, thus reducing the total analysis time and maximizing ease-of-use. In this review, we focus on homogeneous biosensors for the in vitro detection of biomarkers. Within this broad range of biosensors, we concentrate on methods that apply magnetic particle labels. The advantage of such methods lies in the added possibility to manipulate the particle labels by applied magnetic fields, which can be exploited, for example, to decrease incubation times or to enhance the signal-to-noise-ratio of the measurement signal by applying frequency-selective detection. In our review, we discriminate the corresponding methods based on the nature of the acquired measurement signal, which can either be based on magnetic or optical detection. The underlying measurement principles of the different techniques are discussed, and biosensing examples for all techniques are reported, thereby demonstrating the broad applicability of homogeneous in vitro biosensing based on magnetic particle label actuation

Applications, Surface Modification and Functionalization of Nickel Nanorods

The growing number of nanoparticle applications in science and industry is leading to increasingly complex nanostructures that fulfill certain tasks in a specific environment. Nickel nanorods already possess promising properties due to their magnetic behavior and their elongated shape. The relevance of this kind of nanorod in a complex measurement setting can be further improved by suitable surface modification and functionalization procedures, so that customized nanostructures for a specific application become available. In this review, we focus on nickel nanorods that are synthesized by electrodeposition into porous templates, as this is the most common type of nickel nanorod fabrication method. Moreover, it is a facile synthesis approach that can be easily established in a laboratory environment. Firstly, we will discuss possible applications of nickel nanorods ranging from data storage to catalysis, biosensing and cancer treatment. Secondly, we will focus on nickel nanorod surface modification strategies, which represent a crucial step for the successful application of nanorods in all medical and biological settings. Here, the immobilization of antibodies or peptides onto the nanorod surface adds another functionality in order to yield highly promising nanostructures

Homogeneous Biosensing Based on Magnetic Particle Labels

International audienceThe growing availability of biomarker panels for molecular diagnostics is leading to an increasing need for fast and sensitive biosensing technologies that are applicable to point-of-care testing. In that regard, homogeneous measurement principles are especially relevant as they usually do not require extensive sample preparation procedures, thus reducing the total analysis time and maximizing ease-of-use. In this review, we focus on homogeneous biosensors for the in vitro detection of biomarkers. Within this broad range of biosensors, we concentrate on methods that apply magnetic particle labels. The advantage of such methods lies in the added possibility to manipulate the particle labels by applied magnetic fields, which can be exploited, for example, to decrease incubation times or to enhance the signal-to-noise-ratio of the measurement signal by applying frequency-selective detection. In our review, we discriminate the corresponding methods based on the nature of the acquired measurement signal, which can either be based on magnetic or optical detection. The underlying measurement principles of the different techniques are discussed, and biosensing examples for all techniques are reported, thereby demonstrating the broad applicability of homogeneous in vitro biosensing based on magnetic particle label actuatio

Multifunctional Nanostructures and Nanopocket Particles Fabricated by Nanoimprint Lithography

Nanostructured surfaces and nanoparticles are already widely employed in many different fields of research, and there is an ever-growing demand for reliable, reproducible and scalable nanofabrication methods. This is especially valid for multifunctional nanomaterials with physical properties that are tailored for specific applications. Here, we report on the fabrication of two types of nanomaterials. Specifically, we present surfaces comprising a highly uniform array of elliptical pillars as well as nanoparticles with the shape of nanopockets, possessing nano-cavities. The structures are fabricated by nanoimprint lithography, physical and wet-chemical etching and sputter deposition of thin films of various materials to achieve a multifunctional nanomaterial with defined optical and magnetic properties. We show that the nanopockets can be transferred to solution, yielding a nanoparticle dispersion. All fabrication steps are carefully characterized by microscopic and optical methods. Additionally, we show optical simulation results that are in good agreement with the experimentally obtained data. Thus, this versatile method allows to fabricate nanomaterials with specific tailor-made physical properties that can be designed by modelling prior to the actual fabrication process. Finally, we discuss possible application areas of these nanomaterials, which range from biology and medicine to electronics, photovoltaics and photocatalysis

Modeling and Development of a Biosensor Based on Optical Relaxation Measurements of Hybrid Nanoparticles

Schrittwieser S, Ludwig F, Dieckhoff J, et al. Modeling and Development of a Biosensor Based on Optical Relaxation Measurements of Hybrid Nanoparticles. ACS Nano. 2012;6(1):791-801.We present a new approach for homogeneous real-time immunodiagnostics (denoted as "PlasMag") that can be directly carried out in sample solutions such as serum, thus promising to circumvent the need of sample preparation. It relies on highly sensitive plasmon-optical detection of the relaxation dynamics of magnetic nanoparticles immersed in the sample solution, which changes when target molecules bind to the surfaces of the nanoparticles due to the increase in their hydrodynamic radii. This method requires hybrid nanoparticles that combine both magnetic and optical anisotropic properties. Our model calculations show that core shell nanorods with a cobalt core diameter of 6 nm, a cobalt core length of 80 nm, and a gold shell thickness of 5 nm are ideally suited as nanoprobes. On the one hand, the spectral position of the longitudinal plasmon resonance of such nanoprobes lies in the near-infrared, where the optical absorption in serum is minimal. On the other hand, the expected change in their relaxation properties on analyte binding is maximal for rotating magnetic fields as excitation in the lower kHz regime. In order to achieve high alignment ratios of the nanoprobes, the strength of the magnetic field should be around 5 mT. While realistic distributions of the nanoprobe properties result in a decrease of their mean optical extinction, the actual relaxation signal change on analyte binding is largely unaffected. These model calculations are supported by measurements on plain cobalt nanorod dispersions, which are the base component of the aspired core-shell nanoprobes currently under development

Optical biosensor technologies for molecular diagnostics at the point-of-care

International audienceLabel-free optical schemes for molecular biosensing hold a strong promise for point-of-care applications in medical research and diagnostics. Apart from diagnostic requirements in terms of sensitivity, specificity, and multiplexing capability, also other aspects such as ease of use and manufacturability have to be considered in order to pave the way to a practical implementation. We present integrated optical waveguide as well as magnetic nanoparticle based molecular biosensor concepts that address these aspects. The integrated optical waveguide devices are based on low-loss photonic wires made of silicon nitride deposited by a CMOS compatible plasma-enhanced chemical vapor deposition (PECVD) process that allows for backend integration of waveguides on optoelectronic CMOS chips. The molecular detection principle relies on evanescent wave sensing in the 0.85 μm wavelength regime by means of Mach-Zehnder interferometers, which enables on-chip integration of silicon photodiodes and, thus, the realization of system-on-chip solutions. Our nanoparticle-based approach is based on optical observation of the dynamic response of functionalized magneticcore/ noble-metal-shell nanorods (‘nanoprobes’) to an externally applied time-varying magnetic field. As target molecules specifically bind to the surface of the nanoprobes, the observed dynamics of the nanoprobes changes, and the concentration of target molecules in the sample solution can be quantified. This approach is suitable for dynamic real-time measurements and only requires minimal sample preparation, thus presenting a highly promising point-of-care diagnostic system. In this paper, we present a prototype of a diagnostic device suitable for highly automated sample analysis by our nanoparticle-based approach

Towards Recycled Paper Based Impedance Biosensor with Wireless Readout

Results are presented regarding the development of recycled paper based impedance biosensors with screen printed interdigitated electrode structures (IDES). The sensors show a response to increasing salt concentrations in the range 30–100 mM NaCl. To prove the feasibility of using recycled paper, biofunctionalization with a glucose sensitive enzyme mixture was performed by inkjet printing. The quantification of the glucose sensitive colour change reaction in paper was investigated and a trend is found in the range of 6–90 mg/dL. Subsequently, measurements with a wireless electronic readout system were performed on an electrochemical assay showing a decrease of the normalized sensor response dependent from the glucose concentration in the range 0–80 mg/dL

Homogeneous Protein Analysis by Magnetic Core–Shell Nanorod Probes

International audienceStudying protein interactions is of vital importance both to fundamental biology research and to medical applications. Here, we report on the experimental proof of a universally applicable label-free homogeneous platform for rapid protein analysis. It is based on optically detecting changes in the rotational dynamics of magnetically agitated core–shell nanorods upon their specific interaction with proteins. By adjusting the excitation frequency, we are able to optimize the measurement signal for each analyte protein size. In addition, due to the locking of the optical signal to the magnetic excitation frequency, background signals are suppressed, thus allowing exclusive studies of processes at the nanoprobe surface only. We study target proteins (soluble domain of the human epidermal growth factor receptor 2 - sHER2) specifically binding to antibodies (trastuzumab) immobilized on the surface of our nanoprobes and demonstrate direct deduction of their respective sizes. Additionally, we examine the dependence of our measurement signal on the concentration of the analyte protein, and deduce a minimally detectable sHER2 concentration of 440 pM. For our homogeneous measurement platform, good dispersion stability of the applied nanoprobes under physiological conditions is of vital importance. To that end, we support our measurement data by theoretical modeling of the total particle–particle interaction energies. The successful implementation of our platform offers scope for applications in biomarker-based diagnostics as well as for answering basic biology questions