Vasiliki Demas

T2 Magnetic Resonance Enables Nanoparticle-Mediated Rapid Detection of Candidemia in Whole Blood

Nanoparticles and T2 magnetic resonance allow for DNA amplification and detection of Candida species in clinical whole-blood specimens. Nanoparticle Clusters Rapidly Detect Candida Time is not on the side of patients suspected of blood infection (sepsis). Patients with bloodstream infections of Candida species are often misdiagnosed. Or, the diagnosis comes too late. These two factors contribute to a high mortality rate of 40% from this fungus. To deliver a quick and accurate diagnosis for candidemia, Neely and colleagues designed an assay that combines nanotechnology and clinical imaging. The authors developed a nano-inspired platform that detects DNA from five of the most common Candida species found in patient blood. Candida cells were first lysed mechanically, and then polymerase chain reaction primers and a polymerase-like enzyme were added to selectively amplify the released DNA. Nanoparticles with complementary “capture probes” could then bind to the amplified DNA. At that point, the free particles clustered together, allowing for detection with T2 magnetic resonance (T2MR). Neely et al. built a portable T2MR instrument for detecting the fungal DNA at the patient’s bedside. With this technology, they were able to detect down to three colony-forming units (CFU) of C. albicans and C. tropicalis per milliliter of blood; even lower limits of detection (1 to 2 CFU/ml) were observed for C. krusei, C. glabrata, and C. parapsilosis. Using whole-blood samples from 24 patients, the authors were able to correctly identify the 8 candidemic patients, without any false-positive readouts from blood samples that contained bacteria. The combination of nanoparticles and clinical MR detection allowed for specific detection of Candida species in infected patients’ blood. The T2MR readouts were even more sensitive than blood culture, showing residual Candida cells in patients undergoing treatment with antifungal medication days after blood culture tests were negative. With such portability and sensitivity, this nanoparticle platform could be used in the clinic to diagnose blood infection earlier than standard culture, thus allowing for rapid treatment of septic patients, where time is of the essence. Candida spp. cause both local and disseminated infections in immunocompromised patients. Bloodstream infections of Candida spp., known as “candidemia,” are associated with a high mortality rate (40%), which is mainly attributed to the long diagnostic time required by blood culture. We introduce a diagnostic platform based on T2 magnetic resonance (T2MR), which is capable of sensitive and rapid detection of fungal targets in whole blood. In our approach, blood-compatible polymerase chain reaction is followed by hybridization of the amplified pathogen DNA to capture probe–decorated nanoparticles. Hybridization yields nanoparticle microclusters that cause large changes in the sample’s T2MR signal. With this T2MR-based method, Candida spp. can be detected directly in whole blood, thus eliminating the need for analyte purification. Using a small, portable T2MR detection device, we were able to rapidly, accurately, and reproducibly detect five Candida species within human whole blood with a limit of detection of 1 colony-forming unit/ml and a time to result of <3 hours. Spiked blood samples showed 98% positive agreement and 100% negative agreement between T2MR and blood culture. Additionally, performance of the assay was evaluated on 21 blinded clinical specimens collected serially. This study shows that the nanoparticle- and T2MR-based detection method is rapid and amenable to automation and offers clinicians the opportunity to detect and identify multiple human pathogens within hours of sample collection.

Magnetic resonance for in vitro medical diagnostics: superparamagnetic nanoparticle-based magnetic relaxation switches

Advances in magnetic resonance (MR) miniaturization, along with nanoparticles and biotechnology, are extending MR applications in diagnostics to beyond the medical imaging regime. The principles behind magnetic resonance switch (MRSw) biosensors, as well as a summary of rapidly developing fields including MR miniaturization and MRSw demonstrations, are presented here. Due to the range of applications of MRSw biosensor tests and the breakthroughs in downsized instruments, continued development will enable the deployment of MRSw biosensors in a wide variety of settings and with potentially unlimited targets.

Development of a System for Rapid Detection of Contaminants in Water Supplies Using Magnetic Resonance and Nanoparticles

To keep the water supply safe and to ensure a swift and accurate response to a water supply contamination event, rapid and robust methods for microbial testing are necessary. Current technologies are complex, lengthy and costly and there is a need for rapid, reliable, and precise approaches that can readily address this fundamental security and safety issue. T2 Biosystems is focused on providing solutions to this problem by making breakthroughs in nanotechnology and biosensor techniques that address the current technical restrictions facing rapid, molecular analysis in complex samples. In order to apply the T2 Biosystems nucleic acid detection procedure to the analysis of nucleic acid targets in unprocessed water samples, Bacillus thuringeinsis was selected as a model organism and local river water was selected as the sample matrix. The initial assay reagent formulation was conceived with a manual magnetic resonance reader, was optimized using a high throughput system, and transferred back to the MR reader for potential field use. The final assay employing the designed and manufactured instruments was capable of detecting 10 CFU/mL of B. thuringiensis directly within the environmental water sample within 90 minutes. Further, discrimination of two closely related species of Bacilli was accomplished using the methods of this project; greater than 3-fold discrimination between B. cereus and B. thuringiensis at a concentrations spanning 10 CFU/mL to 10{sup 5} CFU/mL was observed.