Irina Perreard

Molecular sensing with magnetic nanoparticles using magnetic spectroscopy of nanoparticle Brownian motion.

Functionalized magnetic nanoparticles (mNPs) have shown promise in biosensing and other biomedical applications. Here we use functionalized mNPs to develop a highly sensitive, versatile sensing strategy required in practical biological assays and potentially in vivo analysis. We demonstrate a new sensing scheme based on magnetic spectroscopy of nanoparticle Brownian motion (MSB) to quantitatively detect molecular targets. MSB uses the harmonics of oscillating mNPs as a metric for the freedom of rotational motion, thus reflecting the bound state of the mNP. The harmonics can be detected in vivo from nanogram quantities of iron within 5s. Using a streptavidin-biotin binding system, we show that the detection limit of the current MSB technique is lower than 150 pM (0.075 pmole), which is much more sensitive than previously reported techniques based on mNP detection. Using mNPs conjugated with two anti-thrombin DNA aptamers, we show that thrombin can be detected with high sensitivity (4 nM or 2 pmole). A DNA-DNA interaction was also investigated. The results demonstrated that sequence selective DNA detection can be achieved with 100 pM (0.05 pmole) sensitivity. The results of using MSB to sense these interactions, show that the MSB based sensing technique can achieve rapid measurement (within 10s), and is suitable for detecting and quantifying a wide range of biomarkers or analytes. It has the potential to be applied in variety of biomedical applications or diagnostic analyses.

The performance of steady-state harmonic magnetic resonance elastography when applied to viscoelastic materials

PURPOSE The clinical efficacy of breast elastography may be limited when the authors employ the assumption that soft tissues exhibit linear, frequency-independent isotropic mechanical properties during the recovery of shear modulus. Thus, the purpose of this research was to evaluate the degradation in performance incurred when linear-elastic MR reconstruction methods are applied to phantoms that are fabricated using viscoelastic materials. METHODS To develop phantoms with frequency-dependent mechanical properties, the authors measured the complex modulus of two groups of cylindrical-shaped gelatin samples over a wide frequency range (up to 1 kHz) with the established principles of time-temperature superposition (TTS). In one group of samples, the authors added varying amounts of agar (1%-4%); in the other group, the authors added varying amounts of sucrose (2.5%-20%). To study how viscosity affected the performance of the linear-elastic reconstruction method, the authors constructed an elastically heterogeneous MR phantom to simulate the case where small viscoelastic lesions were surrounded by relatively nonviscous breast tissue. The breast phantom contained four linear, viscoelastic spherical inclusions (10 mm diameter) that were embedded in normal gelatin. The authors imaged the breast phantom with a clinical prototype of a MRE system and recovered the shear-modulus distribution using the overlapping-subzone-linear-elastic image-reconstruction method. The authors compared the recovered shear modulus to that measured using the TTS method. RESULTS The authors demonstrated that viscoelastic phantoms could be fabricated by including sucrose in the gelation process and that small viscoelastic inclusions were visible in MR elastograms recovered using a linear-elastic MR reconstruction process; however, artifacts that degraded contrast and spatial resolution were more prominent in highly viscoelastic inclusions. The authors also established that the accuracy of the MR elastograms depended on the degree of viscosity that the inclusion exhibited. CONCLUSIONS The results demonstrated that reconstructing shear modulus from other constitutive laws, such as viscosity, should improve both the accuracy and quality of MR elastograms of the breast.

Temperature of the magnetic nanoparticle microenvironment: estimation from relaxation times

Accurate temperature measurements are essential to safe and effective thermal therapies for cancer and other diseases. However, conventional thermometry is challenging so using the heating agents themselves as probes allows for ideal local measurements. Here, we present a new noninvasive method for measuring the temperature of the microenvironment surrounding magnetic nanoparticles from the Brownian relaxation time of nanoparticles. Experimentally, the relaxation time can be determined from the nanoparticle magnetization induced by an alternating magnetic field at various applied frequencies. A previously described method for nanoparticle temperature estimation used a low frequency Langevin function description of magnetic dipoles and varied the excitation field amplitude to estimate the energy state distribution and the corresponding temperature. We show that the new method is more accurate than the previous method at higher applied field frequencies that push the system farther from equilibrium.

Magnetic spectroscopy of nanoparticle Brownian motion measurement of microenvironment matrix rigidity.

Abstract The rigidity of the extracellular matrix and of the integrin links to the cytoskeleton regulates signaling cascades, controlling critical aspects of cancer progression including metastasis and angiogenesis. We demonstrate that the matrix stiffness can be monitored using magnetic spectroscopy of nanoparticle Brownian motion (MSB). We measured the MSB signal from nanoparticles bound to large dextran polymers. The number of glutaraldehyde induced cross-links was used as a surrogate for material stiffness. There was a highly statistically significant change in the MSB signal with the number of cross-links especially prominent at higher frequencies. The p-values were all highly significant. We conclude that the MSB signal can be used to identify and monitor changes in the stiffness of the local matrix to which the nanoparticles are bound.

Magnetic nanoparticles temperature measurements

Magnetic nanoparticles (MNPs) have an ever increasing role in the medical world, particularly in thermal therapies (magnetohypertermia, ablation) for the treatment of cancer. These treatments would benefit of accurate monitoring of the temperature of the MNPs for optimal remedial conditions. It has been shown that the magnetic spectroscopy of nanoparticle Brownian motion (MSB), can be used to measure the temperature of MNPs.

TU‐G‐217A‐07: Magnetic Nanoparticle Quantitation: Compensating for Relaxation Effects

Purpose: Our hypothesis was that the weight of magnetic nanoparticles could be accurately estimated from the magnetic spectroscopy of nanoparticleBrownian motion (MSB) signal. Quantification is critical to bio‐sensing and histology and is becoming more important in medicalimagining. A nanoparticleassay is important in histology and bio‐sensing where antibody targeted magnetic nanoparticles are used to mark specific protein expression. Quantitative imaging of magnetic nanoparticles is also important in applications including hyperthermia and nanoparticledrug delivery. Two factors make quantitative estimates very difficult to achieve: relaxation effects that change the signal produced by each nanoparticle and non‐nanoparticle iron that confuses mass spectroscopy measurements. We introduce a method only sensitive to nanoparticleiron that compensates for relaxation effects that achieves quantitative estimates of the number of magnetic nanoparticles in a sample. Methods: Samples with varying quantities of iron oxide nanoparticles (100 nm mean hydrodynamic diameter) and varying quantities of glycerol were prepared. The samples contained from 1.46 mg to 0.05 mg nanoparticles and from 0% to 27% glycerol. MSB signals were recorded for each sample. The relaxation time was calculated using previously reported methods. The MSB signals were then shifted in frequency to compensate for the change in relaxation time. The scaling of the normalized MSB signal that approximates the reference sample is the weight of nanoparticles present in the sample. The apparatus used was built for 1.5 mL liquid samples; a system for smaller samples would be more sensitive. Results: The RMS percentage error in the weight of nanoparticles was 4.9%. The RMS error in the weight of nanoparticles was 0.018 mg iron. Other sources of iron such as blood did not bias the estimates. Conclusions: The method presented makes accurate MSB estimates of the weight of nanoparticles. Acknowledgement: NIH‐NCI 1U54CA151662‐01 NIH‐NCI 1U54CA151662‐01

Micro-rheology: evaluating the rigidity of the microenvironment surrounding antibody binding sites

The microscopic rigidity of structural elements of the cell and of the extracellular matrix control the genetic expression of factors that control critical aspects of malignancy including metastasis and neoangiogenesis. Methods of measuring the rigidity in vitro are being developed and exploited to explore the mechanisms involved. But no methods that function in vivo are available. We demonstrate proof of concept that the stiffness of the microenvironment surrounding bound magnetic nanoparticles can be measured using the shape of the spectra of the magnetization induced by a harmonic applied field. The microscopic region where the stiffness is measured can be selected by selecting the antibody binding sites for which the nanoparticles are targeted. In other applications, the same signal from the nanoparticles has been measured in vivo at very low concentrations so the methods demonstrated here should be capable of measuring low concentrations in vivo as well. The ability to measure the rigidity in vivo will enable the links between genetic control and rigidity to be explored in the complex in vivo environment for the first time.

In vivo measurement of local biomarker concentrations

The reaction has been explored in vitro in solution and the results for a DNA target are provided in Fig. 2. The 24 base pair DNA target can be found with 100 pM sensitivity. Shorter 20 base pair DNA target molecules bound the NPs together with less affinity so the sensitivity is only 2 nM. DNA molecules with incorrect sequencing produced no change in the MSB signal. Thrombin can also be measured with 4 nM sensitivity and streptavidin with 150 pM sensitivity. These proof of concept experiments demonstrate that the method is feasible for hormone concentrations.