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ConspectusThe modern healthcare system faces an unrelenting threat from microorganisms, as evidenced by global outbreaks of new viral diseases, emerging antimicrobial resistance, and the rising incidence of healthcare-associated infections (HAIs). An effective response to these threats requires rapid and accurate diagnostic tests that can identify causative pathogens at the point of care (POC). Such tests could eliminate diagnostic uncertainties, facilitating patient triaging, minimizing the empiric use of antimicrobial drugs, and enabling targeted treatments. Current standard methods, however, often fail to meet the needs of rapid diagnosis in POC settings. Culture-based assays entail long processing times and require specialized laboratory infrastructure; nucleic acid (NA) tests are often limited to centralized hospitals due to assay complexity and high costs. Here we discuss two new POC tests developed in our groups to enable the rapid diagnosis of infection. The first is nanoPCR that takes advantages of core-shell magnetoplasmonic nanoparticles (MPNs): (i) Au shell significantly accelerates thermocycling via volumetric, plasmonic light-to-heat conversion and (ii) a magnetic core enables sensitive in situ fluorescent detection via magnetic clearing. By adopting a Ferris wheel module, the system expedites multisamples in parallel with a minimal setup. When applied to COVID-19 diagnosis, nanoPCR detected SARS-CoV-2 RNA down to 3.2 copy/μL within 17 min. In particular, nanoPCR diagnostics accurately identified COVID-19 cases in clinical samples (n = 150), validating its clinical applicability. The second is a polarization anisotropy diagnostic (PAD) system that exploits the principle of fluorescence polarization (FP) as a detection modality. Fluorescent probes were designed to alter their molecular weight upon recognizing target NAs. This event modulates the probes' tumbling rate (Brownian motion), which leads to changes in FP. The approach is robust against environmental noise and benefits from the ratiometric nature of the signal readout. We applied PAD to detect clinically relevant HAI bacteria (Escherichia coli, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, and Staphylococcus aureus). The PAD assay demonstrated detection sensitivity down to the single bacterium level and determined both drug resistance and virulence status. In summary, these new tests have the potential to become powerful tools for rapid diagnosis in the infectious disease space. They do not require highly skilled personnel or labor-intensive analyses, and the assays are quick and cost-effective. These attributes will make nanoPCR and PAD well-aligned with a POC workflow to aid physicians to initiate prompt and informed patient treatment.

Contrast agents for magnetic resonance imaging (MRI) improve anatomical visualizations. However, owing to poor image resolution in whole-body MRI, resolving fine structures is challenging. Here, we report that a nanoparticle with a polysaccharide supramolecular core and a shell of amorphous-like hydrous ferric oxide generating strong T1 MRI contrast (with a relaxivity coefficient ratio of ~1.2) facilitates the imaging, at resolutions of the order of a few hundred micrometres, of cerebral, coronary and peripheral microvessels in rodents and of lower-extremity vessels in rabbits. The nanoparticle can be synthesized at room temperature in aqueous solution and in the absence of surfactants, has blood circulation and renal clearance profiles that prevent opsonization, and leads to better imaging performance than Dotarem (gadoterate meglumine), a clinically approved gadolinium-based MRI contrast agent. The nanoparticle's biocompatibility and imaging performance may prove advantageous in a broad range of preclinical and clinical applications of MRI.

The current gold standard for COVID-19 confirmation is RT-PCR, which possesses high sensitivity and specificity, but a long turnaround time has been a drawback. Here, we introduce a nanoPCR platform that can yield breakthroughs in RT-PCR speed and decentralize the diagnostic testing. A key innovation is to exploit magneto-plasmonic nanoparticles for dual purposes: fast thermocycling through plasmonic heating and enhanced signal detection via magnetic fluorescence switch. We further integrated these functionalities into a portable system to streamline point-of-care (POC) COVID-19 diagnostics with a “one-step-finish” approach from sampling to result. When applied with clinical COVID-19 samples, nanoPCR achieved an analytical performance of sensitivity and specificity comparable to that of a benchtop instrument but completed the entire detection within 18 minutes (vs. 2.5 hours for regular RT-PCR), which makes it ideal for rapid POC diagnostics. This platform technology is readily scalable for higher throughput and expandable to other disease targets, promising broader impacts in on-site molecular testing.

Tetrahydrocannabinol (THC), the primary psychoactive ingredient of cannabis, impairs cognitive and motor function in a concentration-dependent fashion. Drug testing is commonly performed for employment and law enforcement purposes; however, available tests produce low-sensitive binary results (lateral flow assays) or have long turnaround (gas chromatography-mass spectrometry). To enable on-site THC quantification in minutes, we developed a rapid assay for oral THC analysis called EPOCH, express probe for on-site cannabis inhalation. EPOCH features distinctive sensor design such as a radial membrane and transmission optics, all contained in a compact cartridge. This integrated approach permitted assay completion within 5 minutes with a detection limit of 0.17 ng/mL THC, which is below the regulatory guideline (1 ng/mL). As a proof of concept for field testing, we applied EPOCH to assess oral fluid samples from cannabis users (n = 43) and controls (n = 43). EPOCH detected oral THC in all specimens from cannabis smokers (median concentration, 478 ng/mL) and THC-infused food consumers. Longitudinal monitoring showed a fast drop in THC concentrations within the first 6 hours of cannabis smoking (half-life, 1.4 hours).

Contrast agents for magnetic resonance imaging (MRI) improve anatomical visualizations. However, owing to poor image resolution in whole-body MRI, resolving fine structures is challenging. Here, we report that a nanoparticle with a polysaccharide supramolecular core and a shell of amorphous-like hydrous ferric oxide generating strong T