| 1. |
- Ahrentorp, Fredrik, et al.
(författare)
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Sensitive magnetic biodetection using magnetic multi-core nanoparticles and RCA coils
- 2017
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Ingår i: Journal of Magnetism and Magnetic Materials. - : Elsevier BV. - 0304-8853 .- 1873-4766. ; 427, s. 14-18
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Tidskriftsartikel (refereegranskat)abstract
- We use functionalized iron oxide magnetic multi-core particles of 100 nm in size (hydrodynamic particle diameter) and AC susceptometry (ACS) methods to measure the binding reactions between the magnetic nanoparticles (MNPs) and bio-analyte products produced from DNA segments using the rolling circle amplification (RCA) method. We use sensitive induction detection techniques in order to measure the ACS response. The DNA is amplified via RCA to generate RCA coils with a specific size that is dependent on the amplification time. After about 75 min of amplification we obtain an average RCA coil diameter of about 1 mu m. We determine a theoretical limit of detection (LOD) in the range of 11 attomole (corresponding to an analyte concentration of 55 fM for a sample volume of 200 mu L) from the ACS dynamic response after the MNPs have bound to the RCA coils and the measured ACS readout noise. We also discuss further possible improvements of the LOD.
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| 2. |
- Blomgren, Jakob, et al.
(författare)
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Development of a sensitive induction-based magnetic nanoparticle biodetection method
- 2018
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Ingår i: Nanomaterials. - : MDPI AG. - 2079-4991. ; 8:11
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Tidskriftsartikel (refereegranskat)abstract
- We developed a novel biodetection method for influenza virus based on AC magnetic susceptibility measurement techniques (the DynoMag induction technique) together with functionalized multi-core magnetic nanoparticles. The sample consisting of an incubated mixture of magnetic nanoparticles and rolling circle amplified DNA coils is injected into a tube by a peristaltic pump. The sample is moved as a plug to the two well-balanced detection coils and the dynamic magnetic moment in each position is read over a range of excitation frequencies. The time for making a complete frequency sweep over the relaxation peak is about 5 minutes (10 Hz–10 kHz with 20 data points). The obtained standard deviation of the magnetic signal at the relaxation frequency (around 100 Hz) is equal to about 10−5 (volume susceptibility SI units), which is in the same range obtained with the DynoMag system. The limit of detection with this method is found to be in the range of 1 pM.
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| 3. |
- Kalaboukhov, Alexei, 1975, et al.
(författare)
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Operation of a high-T-C SQUID gradiometer with a two-stage MEMS-based Joule-Thomson micro-cooler
- 2016
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Ingår i: Superconductor Science and Technology. - : IOP Publishing. - 0953-2048 .- 1361-6668. ; 29:9
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Tidskriftsartikel (refereegranskat)abstract
- Practical applications of high-T-C superconducting quantum interference devices (SQUIDs) require cheap, simple in operation, and cryogen-free cooling. Mechanical cryo-coolers are generally not suitable for operation with SQUIDs due to their inherent magnetic and vibrational noise. In this work, we utilized a commercial Joule-Thomson microfluidic two-stage cooling system with base temperature of 75 K. We achieved successful operation of a bicrystal high-T-C SQUID gradiometer in shielded magnetic environment. The micro-cooler head contains neither moving nor magnetic parts, and thus does not affect magnetic flux noise of the SQUID even at low frequencies. Our results demonstrate that such a microfluidic cooling system is a promising technology for cooling of high-T-C SQUIDs in practical applications such as magnetic bioassays.
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| 4. |
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| 5. |
- Sepehri, Sobhan, 1986, et al.
(författare)
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Characterization of Binding of Magnetic Nanoparticles to Rolling Circle Amplification Products by Turn-On Magnetic Assay
- 2019
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Ingår i: Biosensors-Basel. - : MDPI AG. ; 9:3
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Tidskriftsartikel (refereegranskat)abstract
- The specific binding of oligonucleotide-tagged 100 nm magnetic nanoparticles (MNPs) to rolling circle products (RCPs) is investigated using our newly developed differential homogenous magnetic assay (DHMA). The DHMA measures ac magnetic susceptibility from a test and a control samples simultaneously and eliminates magnetic background signal. Therefore, the DHMA can reveal details of binding kinetics of magnetic nanoparticles at very low concentrations of RCPs. From the analysis of the imaginary part of the DHMA signal, we find that smaller MNPs in the particle ensemble bind first to the RCPs. When the RCP concentration increases, we observe the formation of agglomerates, which leads to lower number of MNPs per RCP at higher concentrations of RCPs. The results thus indicate that a full frequency range of ac susceptibility observation is necessary to detect low concentrations of target RCPs and a long amplification time is not required as it does not significantly increase the number of MNPs per RCP. The findings are critical for understanding the underlying microscopic binding process for improving the assay performance. They furthermore suggest DHMA is a powerful technique for dynamically characterizing the binding interactions between MNPs and biomolecules in fluid volumes.
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| 6. |
- Sepehri, Sobhan, 1986
(författare)
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Differential Magnetic Biosensor using HTS SQUID Gradiometer
- 2019
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- A fundamental tool for containing an epidemic outbreak and mitigating its effects is early diagnostics. Currently, most of the diagnostic tests are performed by trained staff in centralized labs, which are expensive and time-consuming to establish and operate. Lack of access to such facilities could have devastating effects. The principal motivation behind point-of-care diagnostic systems is to provide a low cost, fast, sensitive, and specific test in the field which does not require highly skilled staff to operate. This thesis describes a magnetic biosensor which takes advantage of a high- T c superconducting quantum interference device (SQUID) gradiometer sensor and magnetic nanoparticles (MNPs) to develop a diagnostic unit for point-of-care. Rolling circle amplification (RCA) is used as the primary molecular amplification method. RCA is an isothermal process with very high specificity. It is, therefore, easy to implement in a mix and measure concept of a homogeneous assay. The specific binding of the MNPs to the products of the RCA (i.e., DNA coils) changes their relaxation dynamics which is detected by sensitive ac magnetic susceptibility measurement. One of the issues with homogeneous magnetic assays, which limits their sensitivity, is the presence of excess MNP labels in the test sample solution. To mitigate this problem, a novel technique is introduced, which takes advantage of the geometry of our gradiometer sensor for a differential ac magnetic susceptibility measurement. In this technique, a negative control sample and a positive test sample are measured in a single measurement. The differential measurement virtually removes all of the unbound MNPs in the test sample and is analogous to the physical washing step typically used in conventional assays. This technique also provides better signal to noise ratio (SNR) and can detect target concentrations down to tens of femtomolar levels (45 fM). To eliminate the use of liquid nitrogen (LN2) for cooling of the SQUID sensor (as it is not abundantly available in the field) we have shown the successful operation of a SQUID gradiometer sensor on a commercially available micro-cooler platform. The operation of the SQUID on the micro-cooler and the high sensitivity of the novel differential ac susceptibility technique, realized in this work, are critical steps towards a homogeneous magnetic nucleic acid biosensor for rapid detection of diseases. The methods and instruments that are adopted and presented here are generic and could, in principle, be used for other targets such as Influenza, Ebola, and Zika. With full implementation of the molecular amplification on a disposable lab-on-a-chip, the unit would be promising for rapid and highly sensitive diagnostics at the point-of-care.
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| 7. |
- Sepehri, Sobhan, 1986, et al.
(författare)
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Homogeneous Differential Magnetic Assay
- 2019
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Ingår i: Acs Sensors. - : American Chemical Society (ACS). - 2379-3694. ; 4:9, s. 2381-2388
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Tidskriftsartikel (refereegranskat)abstract
- Assays are widely used for detection of various targets, including pathogens, drugs, and toxins. Homogeneous assays are promising for the realization of point-of-care diagnostics as they do not require separation, immobilization, or washing steps. For low concentrations of target molecules, the speed and sensitivity of homogeneous assays have hitherto been limited by slow binding kinetics, time-consuming amplification steps, and the presence of a high background signal. Here, we present a homogeneous differential magnetic assay that utilizes a differential magnetic readout that eliminates previous limitations of homogeneous assays. The assay uses a gradiometer sensor configuration combined with precise microfluidic sample handling. This enables simultaneous differential measurement sample containing a synthesized Vibrio cholerae target and a negative control sample, which reduces the background signal and increases the readout speed. Very low concentrations of targets down to femtomolar levels are thus detectable without any additional amplification of the number of targets. Our homogeneous differential magnetic assay method opens new possibilities for rapid and highly sensitive diagnostics at the point of care.
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| 8. |
- Sepehri, Sobhan, 1986
(författare)
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Ultra-sensitive measurements of magnetically labelled RCA products in a microfluidic channel using a high-Tc SQUID
- 2018
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The development of a nucleic acid (deoxyribonucleic acid (DNA), ribonucleic acid (RNA)) bioassay based on magnetic nanoparticles (MNPs) with a high-Tc superconducting quantum interference device (SQUID) gradiometer as a magnetic readout is described. The specific binding of the MNPs to the target DNA molecules changes the MNPs size distribution and, therefore, the relaxation dynamics and is measured by magnetic ac susceptometry. The binding reactions are measured by SQUID gradiometer in a microfluidic channel with volume of 3 μL. The magnetic content sensitivity at the noise level of our SQUID is estimated to be 1.5e6 MNPs/sqrt(Hz) or 2.9e-10 emu/sqrt(Hz) in magnetic moment, corresponding to 2.5 ng of MNPs with diameter of 100 nm. Two different assay protocols are investigated for a magnetic nucleic acid biosensor. Padlock probes with suitable sequences are used as bioreceptors and circularize upon target recognition. The rolling circle amplification (RCA) provides the gain to the target molecule by copying the circularized padlock probe into a large concatemer. The specific binding of the MNPs to these large DNA coils changes their relaxation dynamics. These large DNA molecules can also digest into short monomers. The monomers can induce an agglutination if two MNP with matching sequence motifs to the two ends of the monomer are introduced. The agglutinated clusters would have large hydrodynamic size, thus, a different relaxation dynamics. The bioassay has shown higher sensitivity using large DNA coils. Extrapolated sensitivity of the sensor to target analyte is estimated to be 66 fM of RCA coils. This is limit is equivalent to 1.0e5 target DNA molecules. The method and instruments that are adopted and presented here are not limited to the Vibrio cholera bioanalyte and are generic and could in principle be used for other DNA or RNA viruses. The ultra-high magnetic sensitivity combined with the microfluidic sample handling is a critical step towards a magnetic bioassay for rapid detection of diseases at the point-of-care (POC). Future developments include implementation of all steps of the bioassay on a disposable lab-on-chip and eliminating the liquid nitrogen by operating the SQUID on a micro-cooler platform. These would make the magnetic bioassay promising for applications as a future nano-diagnostics unit.
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| 9. |
- Sepehri, Sobhan, 1986, et al.
(författare)
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Volume-amplified magnetic bioassay integrated with microfluidic sample handling and high-Tc SQUID magnetic readout
- 2018
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Ingår i: APL Bioengineering. - : AIP Publishing. - 2473-2877. ; 2:1
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Tidskriftsartikel (refereegranskat)abstract
- A bioassay based on a high-Tc superconducting quantum interference device (SQUID) reading out functionalized magnetic nanoparticles (fMNPs) in a prototype microfluidic platform is presented. The target molecule recognition is based on volume amplification using padlock-probe-ligation followed by rolling circle amplification (RCA). The MNPs are functionalized with single-stranded oligonucleotides, which give a specific binding of the MNPs to the large RCA coil product, resulting in a large change in the amplitude of the imaginary part of the ac magnetic susceptibility. The RCA products from amplification of synthetic Vibrio cholera target DNA were investigated using our SQUID ac susceptibility system in microfluidic channel with an equivalent sample volume of 3 μl. From extrapolation of the linear dependence of the SQUID signal versus concentration of the RCA coils, it is found that the projected limit of detection for our system is about 1.0 e5 RCA coils (0.2e−18 mol), which is equivalent to 66 fM in the 3 μl sample volume. This ultra-high magnetic sensitivity and integration with microfluidic sample handling are critical steps towards magnetic bioassays for rapid detection of DNA and RNA targets at the point of care.
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