Nanogold Catches Disease in 15 Minutes: NasRED Reads Hundreds of Molecules in a Drop of Blood

ACS Nano described a portable diagnostic test called NasRED ( Nanoparticle-Supported, Rapid, Electronic Detection ): it uses gold nanoparticles and electro-optical reading to detect antigens and antibodies to infections at super-low concentrations — down to the subfemtomolar/attomolar level. Testing for COVID-19 showed accurate discrimination from other infections, response time was ~15 minutes, and the cost of the test was about $2. According to the authors, sensitivity is ~3000 times higher than ELISA, 16 times less sample is required, and the result is 30 times faster.

Background

• Why PoC diagnostics again and how to measure its success. In real practice, point-of-care tests are needed (on-site, fast, cheap) that meet the ASSURED/REASSURED criteria: Affordable, Sensitive, Specific, User-friendly, Rapid/Robust, Equipment-free/simple, Delivered plus Real-time connectivity and ease of sample collection. Most "home" tests still do not cover all the points, especially "S" - sensitivity. Hence the race for methods that will provide a laboratory level of sensitivity without a laboratory.
• Where the classics get stuck.
  • LAT strips (antigen tests) are fast and cheap, but sensitivity against PCR is moderate and highly dependent on viral load/time of illness; even the best kits often fall short of “laboratory” sensitivity.
  • ELISA is accurate but requires reagents, washers/readers, incubations - this is hours and a laboratory; existing "enhanced" versions lower thresholds, but at the cost of protocol complexity. For field screening, these are barriers.
• Why gold nanoparticles? AuNPs are the workhorse of biosensors: they have a pronounced plasmonic response (absorption/scattering changes upon aggregation or when the environment changes), convenient surface chemistry for protein/aptamer conjugation, and good stability. This allows for the construction of tests where the “analyzed molecule ↔ nanoparticle” link is converted into an optical/electronic signal without complex optics.
• Electro-/Opto-Electronic Readout as a Step Forward. The key to PoC is to simplify detection: instead of large spectrophotometers, use an LED + simple photosensor/electronics and read the change in transparency/scattering or “settling” of functionalized nanoparticles upon target binding. Such schemes provide a large dynamic range and fast response time while maintaining low detection limits. This is where NasRED fits in.
• Why is it important to be able to see both antigens and antibodies? For infections at different stages, some targets are more informative than others: antigen for early active infection, antibodies for the fact of past/current infection with seroconversion or assessment of the immune response. Platforms that modularly “requalify” from antigens to antibodies (and back) scale up faster for new pathogens/tasks.
• The context of this particular article. In a demonstration on SARS-CoV-2, NasRED demonstrated detection of subfemtomolar levels of antigens/antibodies in ~15 minutes from a microvolume (about 6 µl) and accurate discrimination of COVID-19 from other infections; the platform is claimed to be adaptable to toxins, tumor markers, etc. This closes the gap between the “strip” and the lab in sensitivity and speed. The consequence is the potential for early detection at low prevalence and in low-resource settings.
• But hypersensitivity also comes with risks. The lower the threshold, the greater the requirements for purity, cross-reaction control, and false-positive management. Therefore, each new “target” on the platform requires separate clinical validations and stress testing for matrix effects (blood, saliva, nasopharynx) and the stability of consumables in real supply chains.
• Why this is a logical direction for the evolution of tests. The field has already learned to "break" picomolar barriers (digital ELISA, enhanced LF formats), but more often at the cost of expensive equipment/complex protocols. AuNP platforms with simple electronic reading seek to combine ultra-sensitivity with cheap hardware - exactly what the ASSURED/REASSURED criteria require.

How does this work

• Gold nanoparticles are coated with recognition molecules. To search for a viral protein, antibodies are used; to catch the patient's antibodies, viral antigens are used.
• These particles are added to a tiny sample (a drop of blood/saliva/nasal fluid). If the sample contains a target, most of the nanoparticles stick together and settle to the bottom of the tube. If there is no target, the suspension remains cloudy.
• The device passes an LED beam through the top of the liquid and an electronic sensor measures how much light passes through: more light = particles have “fallen”, meaning there is a target. All without bulky optics and complicated sample preparation.

What exactly was shown in the new work

• COVID-19: NasRED reliably detected SARS-CoV-2 antigens and antibodies at levels where standard methods fail, and differentiated COVID-19 from other infections. In wet tests with whole coronavirus particles, sensitivity was comparable to Abbott ID NOW (a popular molecular test), but with an advantage in speed/simplicity.
• Detection threshold: The team pushed sensitivity into the attomolar range (example from the press release: "a drop of ink in 20 Olympic swimming pools"). The title of the article emphasizes the subfemtomolar level.
• Modularity: the same “empty” nanoplatforms can be quickly reprogrammed for other targets, from E. coli (Shiga toxin) to tumor markers and Alzheimer’s proteins; a prototype of this technology previously caught Ebola from tiny volumes of blood.

Why is this important?

• Lab-grade testing — without the lab. A pressing healthcare need is fast, accurate, low-cost point-of-care (PoC) testing. NasRED bridges the gap between rapid strips and “heavy” lab: ~$2 per test, ~15 minutes, minimal equipment and training. This is critical for field conditions and low-resource regions.
• Early detection at low prevalence. When cases are few (early outbreaks, HIV/HCV risk groups, borreliosis), it is not profitable to launch laboratory chains, and patients are simply not tested. The ultra-sensitive PoC test allows you to look for a needle in a haystack — and do it right on the spot.

How much is this "better than standard"?

The authors provide comparisons: ≈3000× more sensitive than ELISA, 16× smaller sample volume, 30× faster response time; in absolute concentrations, hundreds of molecules in sub-microliters, “almost 100,000 times more sensitive than standard laboratory tests” (estimate from institutional release). These numbers refer to benchmarks under study conditions and require external validation.

What is already clear about the "pain points"

• For now, sample preparation requires benchtop mini-centrifuges/mixers; the team is working on miniaturization and automation, with the goal of a fully pocket-sized format and, potentially, a home test.
• The stated universality (modules for different diseases) is excellent on paper, but for the clinic, separate clinical trials are needed for each analytical target (HIV, HCV, borreliosis, etc.) with testing of cross-reactions, reagent stability and supply chain quality.

Where can this go?

In the foreseeable future, NasRED looks like a platform: one device + replaceable sensor “attachments” for the desired marker. If modularity is confirmed, this approach could speed up the deployment of tests for new outbreaks and expand PoC diagnostics in clinics, emergency departments, mobile points, and even in mobile teams for hard-to-reach groups.

Source: Choi Y. et al. Nanoparticle-Supported, Rapid, and Electronic Detection of SARS-CoV-2 Antibodies and Antigens at the Subfemtomolar Level. ACS Nano, published August 11, 2025. https://doi.org/10.1021/acsnano.5c12083