A NOVEL APPROACH TO MAGNETIC
FIELD BIOSENSORS: NMR AND SQUID
DETECTION
A. Valsesiaa, P. Colpoa, F. Rossia, P. Arosiob, M. Marianic,d, M. Cortic, d, M.F. Casulae, A. Lascialfarib,c, d
European Commission, Joint Research Center, IHCP, Ispra (VA), Italy
b Department of Molecular Sciences Applied to Biosystems - DISMAB , Università degli Studi di Milano, Milano, Italy
c Department of Physics “Volta”, University of Pavia, Pavia, Italy
d S3-CNR-INFM, Modena, Italy
e Dipartimento di Scienze Chimiche, Università di Cagliari, Cagliari, Italy
a
Introduction
We have studied novel approaches for the realization of Magnetic Field Effect Biosensors (MFBs), by optimizing the
technique of immobilization of biomolecular probes on the surface and in the bulk. By using maghemite nanoparticles for
marking the biomolecules, we obtained a good sensitivity of the detection method of MFBs using Nuclear Magnetic
Resonance (NMR) and SQUID.
MFBs: Approach 1
Fe2O3-c-PMA-c-Biotin
Streptavidin
AbIgG-c-Biotin
IgG
BSA
ppAA
• Plasma Deposited Poly Acrylic Acid (ppAA) [1]
• Adsorption of human IgG
• Blocking of the unreacted surface groups by BSA
• Reaction with biotinated Ab-IgG molecules at different concentrations
• Absorption of streptavidin
• Absorption of biotinated modified γ-Fe2O3 superparamagnetic nanoparticles [2]
Magnetization Measurements
SQUID
QCM test
IgG
AbIgG
Strept
Fe2O3
14
0.5
hydrodynamic diameter = 270 nm
QCM measurements:
•Frequency shift as a function of the biotinated Ab-IgG molecules
concentration
10
8
SQUID measurements:
6
4
* Room temperature
0.3
0.2
0.1
0.0
0
2
* Constant magnetic field H = 500 Oe
0
Ch1
AbIgG=0
Ch2
Ch3
AbIgG=30 AbIgG=50
10
20
30
40
AbIgG-biotin concentration
0.4
Ch4
hydrodynamic diameter = 200 nm
AbIgG=100
H = 500G
0.3
Magnetic data depend on the concentration of Ab-IgG molecules blocked
on the surface. The magnetic moment increases in presence of γ-Fe2O3
with respect to the substrate +(protein) probe. This represents the
method of detection on which MFB ( biochips ! ) are based.
! Specific biological recognition !
mw(10^-6emu/mg)
DeltaF(Hz)
12
H = 500G
0.4
mw(10^-6emu/mg)
16
0.2
0.1
0.0
0
10
20
30
40
50
60
70
80
AbIgG-biotin concentration
90
100
MFBs: Approach 2
Streptavidin
• Hydrogel of Agarose (1%) directly prepared in the glass tube for NMR measurements
• Diffusion of biotinated modified γ-Fe2O3 superparamagnetic nanoparticles with mild
shaking
• Diffusion of streptavidin with mild shaking
Agarose
NMR Measurements (preliminary results)
Fe2O3-c-PMA-c-Biotin
1H-NMR
relaxation times of the Agarose gel
• at 20.1 MHz: T1 = 2.92 sec.; T2 = 98 msec.
• at 41 MHz: T1 = 2.90 sec.; T2 = 103 msec.
* Room temperature
* 1H-NMR relaxation times T1 and T2 evaluated at 20.1 and 41 MHz as a function of time after the addition of streptavidin in
Agarose gel where biotinated modified γ-Fe2O3 superparamagnetic nanoparticles were included
• Different relaxation times adding streptavidin with respect to np-hydrogel =>
Sensitivity of NMR
The longitudinal relaxation time T1 is weakly influenced by addition of streptavidin to gel with biotinated modified γ-Fe2O3
but ………..
a 10-15% change of the transverse relaxation time T2  method of detection of probe-analyte interaction
Concluding remarks
Two different novel approaches for the realization of Magnetic Field Effect Biosensors (MFBs) based on SQUID
magnetometry and Nuclear Magnetic Resonance detection were developed. Immobilizing biomolecular probe on
functionalized surface ( BIOCHIPS ! ), the specific biological recognition biotin-streptavidin was obtained by means
of SQUID magnetic measurements. Very interesting perspectives using 1H-NMR detection technique on “bulk”
probes were presented.
[1] F. Bretagnol, A. Valsesia, G. Ceccone, P. Colpo, D. Gilliland, L. Ceriotti, M. Hasiwa, and F. Rossi Plasma Processes
and Polymers 3, 443 (2006).
[2] C. J. Lin, R. A. Sperling, J. K. Li, T. Yang, P. Li, M. Zanella, W. H. Chang, and W. J. Parak Small 4, 334 (2008).
Acknowledgments
Fondazione Cariplo is gratefully acknowledged for having
funded the project