The Peer-Reviewed Paper Our Fluorescence Method Is Based On

When people hear we detect microplastics using fluorescence imaging, the first question is always the same: "Is that real science?"

Fair question. Most environmental labs use machines that cost $200,000+ — Fourier-transform infrared spectrometers (FTIR), Raman spectroscopes, pyrolysis-GC/MS systems. Equipment that fills a room and requires a PhD to operate.

So how can a blue light, an orange filter, and a camera do the same job?

It turns out a research team asked the exact same question a few years ago — and published the answer in a peer-reviewed journal. That paper is what our protocol is based on.

One thing to be clear about up front: we're citing this paper because it's where the method comes from, not because the authors endorse us. They haven't reviewed, tested, or validated this kit. Any institutional name that appears below is historical affiliation of the authors when they published, not a partnership.

The Paper

In 2022, Leonard et al. published "Smartphone-enabled rapid quantification of microplastics" in the Journal of Hazardous Materials Letters (DOI: 10.1016/j.hazl.2022.100052). At the time, the authors were working at UCLA's Ozcan Research Lab.

Here's what they did:

1. Isolated microplastics from environmental samples using density separation and vacuum filtration
2. Stained them with Nile Red, a fluorescent dye that binds selectively to synthetic polymers
3. Imaged the results with a smartphone camera using a fluorescence microscope attachment
4. Quantified particles automatically using an image processing algorithm

The result: reliable detection and quantification of microplastics as small as 10 microns — roughly one-tenth the width of a human hair. The entire process takes about an hour per sample, compared to the multi-day workflows required by traditional analytical chemistry methods.

Why This Matters

The Leonard et al. paper didn't just show that smartphone-based fluorescence imaging works. It showed that it eliminates two of the biggest bottlenecks in microplastic analysis:

No chemical digestion required. Traditional methods often require dissolving organic matter with strong acids or alkalis before you can count plastic particles. The fluorescence approach skips this entirely — Nile Red makes plastic glow while everything else stays dark.

No manual counting under a traditional microscope. The fluorescence signal is strong enough that an algorithm (or a trained human eye) can identify and count particles from a photograph. You don't need to sit at an eyepiece for hours classifying each speck.

This is why fluorescence imaging has been called a "rapid-screening" method by the research community. It trades the polymer-by-polymer identification of FTIR for speed and accessibility — while maintaining accuracy for the question most people actually care about: how much plastic is in my water?

Our Method vs. the Leonard et al. Protocol

The physics are identical. Here's how our protocol compares to what's in the paper:

Step	Leonard et al. 2022	The Water Map
Sample prep	Density separation + vacuum filtration	Vacuum filtration through 0.45μm membrane
Staining	Nile Red	Nile Red
Excitation	Blue light (~470nm) via smartphone attachment	Blue light (450-490nm) via fluorescence microscope
Emission filter	Orange longpass filter	Orange emission filter (520nm+)
Imaging	Smartphone camera with 3D-printed opti-mechanical attachment	Fluorescence microscope with standardized magnification
Quantification	Automated algorithm	Manual count from fluorescence image
Detection limit	~10μm	Sub-micron (0.45μm filter)

The core innovation in the paper was the custom 3D-printed attachment that turns a smartphone into a fluorescence microscope. We use a dedicated fluorescence microscope, which gives us more control over magnification and exposure — but the underlying detection mechanism is exactly the same: blue light excites Nile Red, plastic fluoresces, everything else doesn't.

What Fluorescence Imaging Can and Can't Do

It can:

• Detect all major plastic polymer types (polyethylene, polypropylene, polystyrene, PET, nylon, etc.)
• Quantify particles down to 10μm (reported in the Leonard et al. paper) or sub-micron (our filtration)
• Process samples in about an hour
• Produce visual evidence — you can see the plastic in the image

It cannot:

• Identify the specific polymer type of each particle (that requires FTIR or Raman spectroscopy)
• Detect rubber particles — Nile Red does not bind effectively to rubber polymers
• Distinguish between different sources of the same polymer
• Count nanoplastics — particles smaller than ~1 micrometer are below the resolution of an optical microscope

For our purposes — answering "how much microplastic is in your tap water?" — this is the right tradeoff. You get a fast, reliable, visual answer. If someone wants polymer-level identification, that's a different (and much more expensive) test.

The optical boundary: micro vs. nano

It's worth being precise about what fluorescence microscopy measures. Microplastics run from 1 micrometer to 5 millimeters. Nanoplastics are smaller than 1 micrometer — and that's below what visible light can resolve. No optical method, ours included, counts individual nanoplastics. Seeing them takes lab instruments: pyrolysis-GC/MS, stimulated Raman scattering, or electron microscopy.

That boundary doesn't make the microplastic count less useful — it makes it a proxy. The micro and nano fractions come from the same sources (the same pipes, the same bottles, the same supply), so a high microplastic count signals a larger invisible nanoplastic load underneath it. When Columbia ran bottled water through stimulated Raman scattering in 2024, roughly 90% of the ~240,000 particles per liter were nanoplastics — 10 to 100 times more than older optical counts had found. We count what we can see clearly and accurately, and we're upfront that the part you can't see is the part the newest health research is most worried about.

The Bigger Picture

What's happening in microplastic detection right now is what happened with DNA sequencing, blood glucose monitoring, and pregnancy testing before it. Techniques that once required a lab are moving into the field — and eventually into people's homes.

The Leonard et al. paper is one proof point. There are others: the NOAA Marine Debris Program has published protocols for Nile Red fluorescence screening. Maes et al. (2017) demonstrated the method for marine samples. Shim et al. (2016) demonstrated it for quantification.

We're not doing something exotic. We're applying a published screening method to a question nobody else is systematically answering for residential tap water.

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If you want to run this method on your own water, use an at-home microplastics test kit — $50, two tests per kit, and you stain, filter, and count the particles yourself in about 15 minutes. Every result gets added to the map — building the first open dataset of microplastic contamination in LA's drinking water.

References:

• Leonard, J., Koydemir, H.C., Koutnik, V.S., Tseng, D., Ozcan, A., & Mohanty, S.K. (2022). Smartphone-enabled rapid quantification of microplastics. Journal of Hazardous Materials Letters, 3, 100052. DOI: 10.1016/j.hazl.2022.100052
• Leonard, D.J. (2021). Smartphone-Enabled Quantification of Microplastics [Master's thesis, UCLA].
• Maes, T. et al. (2017). A rapid-screening approach to detect and quantify microplastics based on fluorescent tagging with Nile Red. Environmental Science & Technology, 51(24), 14149-14158.
• Shim, W.J. et al. (2016). Identification and quantification of microplastics using Nile Red staining. Marine Pollution Bulletin, 113(1-2), 469-476.