The Core Reaction
FluoroSpec detects lead through a rapid in-situ perovskite formation reaction. Methylammonium bromide (MABr, CH₃NH₃Br) dissolved in isopropanol is applied to a surface. If lead ions (Pb²⁺) are present, they react immediately with the methylammonium (CH₃NH₃⁺) and bromide (Br⁻) ions to nucleate lead halide perovskite quantum dots:
CH₃NH₃Br + PbX₂ → CH₃NH₃PbBr₃ + X⁻
Where X is the original anion of the lead compound (carbonate, sulfate, oxide, etc.). Reaction proceeds at room temperature in seconds.
The resulting CH₃NH₃PbBr₃ (methylammonium lead tribromide) nanocrystals are perovskite quantum dots, semiconducting particles with a direct bandgap tuned by their size and composition. Under 365 nm ultraviolet light, these quantum dots absorb the UV photons and re-emit bright green light at approximately 530 nm with a narrow emission bandwidth (~20 nm FWHM) and high quantum yield.
Reagent
MABr
methylammonium bromide
Product
CH₃NH₃PbBr₃
MAPbBr₃ perovskite
UV Excitation
365 nm
standard UV lamp
Emission Peak
~530 nm
bright green
LOD (paper)
1 ng
0.05 ng/mm² surface
Reaction time
< 5 sec
visible immediately
Step-by-Step: What Happens During a Test
-
Reagent contact: A small drop of MABr-in-isopropanol solution lands on the painted or glazed surface. Isopropanol is a thin, fast-evaporating carrier, nearly invisible.
-
Lead dissolution: Lead compounds at the surface (primarily lead carbonate, PbCO₃, in vintage lead paint; also lead chromate, lead oxide, or other forms) partially dissolve into Pb²⁺ ions in the thin liquid film. Even trace Pb²⁺ at the surface is sufficient.
-
Nucleation: Pb²⁺ ions combine with CH₃NH₃⁺ and Br⁻ ions in solution. The three-dimensional perovskite crystal lattice [PbBr₆]⁴⁻ octahedra form spontaneously, with CH₃NH₃⁺ filling the A-site voids. Quantum confinement effects emerge as the nanocrystals grow.
-
Fluorescence: Under 365 nm UV illumination, the MAPbBr₃ quantum dots absorb photons across their direct bandgap (~2.3 eV) and emit at ~530 nm with high quantum yield. The glow is locked to the painted decoration, only where lead is present.
-
Readout: Bright green fluorescence = lead detected. No fluorescence = lead not detected. The signal is visible to the naked eye within seconds.
Why Only Lead? Selectivity of the MAPbBr₃ System
The perovskite ABX₃ crystal structure imposes strict geometric and electronic constraints. Only ions of the right ionic radius and electronic configuration can occupy the B-site within the [BX₆]⁴⁻ octahedral cage. Lead (Pb²⁺), with its ionic radius of 119 pm and 6s² lone pair, is ideally suited to the bromide perovskite lattice.
Other Heavy Metals Don't Form This Perovskite
Common interferents including cadmium (Cd²⁺), mercury (Hg²⁺), zinc (Zn²⁺), copper (Cu²⁺), and arsenic (As³⁺/As⁵⁺) do not form the same fluorescent MAPbBr₃ structure under these conditions. They may form other compounds, or the reaction simply doesn't proceed to yield the bright green quantum-confined emitter.
This selectivity is not absolute, very high concentrations of competing cations can affect the signal, but under real-world consumer testing conditions (paints, glazes, jewelry, toys), the method is highly selective for Pb²⁺.
Works on All Major Lead Compound Forms
Lead carbonate (PbCO₃), white lead, the dominant pigment in pre-1978 house paint, reacts readily because carbonate is a labile anion. Lead chromate (PbCrO₄, chrome yellow), lead oxide (PbO, litharge), and lead sulfate (PbSO₄) also react, though dissolution kinetics vary. Even sulfhydryl-bound (organically chelated) lead forms the perovskite, as demonstrated by Wang et al. (2020).
Why Perovskite Quantum Dots Glow So Brightly
MAPbBr₃ is a direct-bandgap semiconductor. Unlike indirect-gap materials (silicon, germanium), direct-gap semiconductors emit photons efficiently without requiring phonon assistance. The quantum dot confinement effect further narrows and brightens the emission, as crystal size decreases toward the Bohr exciton radius, the effective bandgap increases and the density of states sharpens, producing the characteristically intense, narrow-bandwidth green emission.
Lead halide perovskites are exceptional among quantum dot materials for their defect tolerance: the [PbBr₆]⁴⁻ octahedral sublattice accommodates defects without creating mid-gap trap states that would quench photoluminescence. This means the quantum dots form quickly, in impure in-situ conditions, and still glow brightly, ideal for a field-deployable test.
"Methylammonium lead bromide perovskite… exhibits a sharp green emission peak at ~530 nm with a full-width at half-maximum of ~20 nm and a photoluminescence quantum yield exceeding 70% in solution."
, Yan et al. (2019), Scientific Reports, doi:10.1038/s41598-019-53297-0
Prior Art and Scientific History
This detection method is based on published, peer-reviewed science that predates any commercial product:
| Publication |
Key Finding |
Relevance |
Yan et al. 2019
Sci. Rep. 9, 16875 |
MABr + Pb²⁺ → CH₃NH₃PbBr₃ QDs, bright green fluorescence at 365 nm, 1 ng LOD on paper strips |
Established the core detection method; primary prior art in USPTO rejection of App 18/285,431 |
Holtus et al. 2018
Nature Chem. 10, 740 |
Carbonate minerals undergo shape-preserving transformation to lead halide perovskites |
Demonstrates lead carbonate (paint pigment) converts directly to perovskite under MABr conditions |
| Wang et al. 2020 |
MAPbBr₃ perovskite formation for sulfhydryl-bound lead detection |
Method works even on chemically chelated lead, the most resistant form |
| Zhang et al. 2017 |
Perovskite lead detection chemistry |
Additional foundational prior art |
The USPTO's Non-Final Office Action on Application 18/285,431 (March 2026) confirmed that all claims on the Lumetallix patent application are anticipated by or obvious over Yan et al. 2019.
Detection Limits and Real-World Performance
Academic studies have characterized the sensitivity of the MABr perovskite method under controlled conditions. In practice, performance depends on reagent concentration, drop volume, surface porosity, and the chemical speciation of lead on the test substrate.
| Parameter |
Value |
Conditions |
| Limit of detection (paper) |
1 ng Pb total; 0.05 ng/mm² |
Yan 2019, paper substrate, 365 nm UV |
| EPA XRF positive threshold |
1.0 mg/cm² |
U.S. regulatory standard for lead paint |
| FluoroSpec visual threshold |
Sub-regulatory trace detection |
Consumer safety screening |
| Reaction temperature |
Room temperature |
No heating required |
| UV source |
365 nm (long-wave UV) |
Included with FluoroSpec kit |
FluoroSpec's higher MABr concentration relative to competing products drives the perovskite formation equilibrium further toward completion, improving signal strength at low lead loadings, the cases that matter most for consumer safety.
Test for Lead at Home
FluoroSpec brings this peer-reviewed chemistry to a precision drip-tip bottle you can use on dishes, toys, paint, jewelry, and more. No lab required, results in seconds under UV.
Shop FluoroSpec
References
- Yan, D. et al. "Determination of lead(II) via methylammonium lead bromide perovskite quantum dots formed from methylammonium bromide." Sci. Rep. 9, 16875 (2019). doi:10.1038/s41598-019-53297-0
- Holtus, T. et al. "Shape-preserving transformation of carbonate minerals into lead halide perovskites." Nature Chem. 10, 740–745 (2018). doi:10.1038/s41557-018-0064-1
- Wang et al. (2020), Sulfhydryl-bound lead detection via MAPbBr₃ perovskite.
- Zhang et al. (2017), Perovskite lead detection chemistry.
- Protesescu, L. et al. "Nanocrystals of Cesium Lead Halide Perovskites." Nano Lett. 15, 3692–3696 (2015). doi:10.1021/acs.nanolett.5b00985
- USPTO Application 18/285,431, Non-Final Office Action (March 2026); full examination record ·