The set-up of a high temperature superconductor radio-frequency SQUID microscope for magnetic nanoparticle detection

Abstract

SQUID (superconducting quantum interference device) microscopes are versatile instruments for biosensing applications, in particular for magnetic nanoparticle detection in immunoassay experiments. We are developing a SQUID microscope based on an HTS rf SQUID magnetometer sensor with a substrate resonator. For the cryogenic setup , a configuration was realized in which the cryostat is continuously refilled and kept at a constant liquid nitrogen level by an isolated tube connection to a large liquid nitrogen reservoir. The SQUID is mounted on top of a sapphire finger, connected to the inner vessel of the stainless steel cryostat. The vacuum gap between cold SQUID and room temperature sample is adjusted by causing precise approach of a 50 µm thin sapphire window using a single fine thread wheel. We investigated possible sensing tip configurations and different sensor integration techniques in order to achieve an optimized design. A new scheme of coupling the rf SQUID from its back to a SrTiO 3 substrate resonator was adopted for the purpose of minimization of the sensor-to-sample spacing. By SQUID substrate thinning and washer size reduction, the optimum coupling conditions for back coupling were determined for different rf SQUID magnetometers prepared on LaAlO 3 and SrTiO 3 substrates. The SQUID microscope system is characterized with respect to its spatial resolution and its magnetic field noise. The SQUID microscope instrument will be used for magnetic nanoparticle marker detection.

STM-SQUID Probe Microscope Based on an RF SQUID Magnetometer

“…Note that this configuration is different from the optimum configuration of the direct-detection-type rf SQUID microscope [15]. A readout coil made of 0.2-mm-thick Cu wire (single turn, 5 mm diameter) is fixed on the substrate resonator.…”

“…In the last decade, various types of SQUID microscope have been studied [1]- [15]. The spatial resolution of these microscopes varies from a few to hundreds of , and is limited by the size of the pickup loop and the sample-sensor distance.…”

Signal enhancement techniques for rf SQUID based magnetic imaging systems

“…The high field sensitivity of high T c rf SQUIDs is associated with their large area layout; this area inherently hinders achieving high spatial resolution. The washer area of the rf SQUIDs must be optimized for the minimum area needed for efficient coupling to the rf coupling circuit [5]. As a replacement for the conventional LC tank circuit, which not only provides less V spp but also takes more space, thus hindering the front-end assembly, thin film superconducting coplanar resonators were used and investigated in the flip chip configuration [7,8].…”

The single crystal superconducting Bi-2212 whiskers fabrication and their thermal transport properties

“…They have also significant potential to use as SQUID or microwave radiation detectors and high speed switching gates [4][5].…”