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Abstract

Biolasers based on biological and biocompatible materials have emerged as powerful tools
for biomedical applications such as cell barcoding, tracking, and biosensing. Despite these
advances, the realization of lasers fabricated entirely from edible substances has remained
largely unexplored. Developing such microlasers could enable optical tagging and sensing
directly within consumable products, thereby overcoming the limitations of conventional
barcodes and sensors, which are restricted to external packaging and vulnerable to removal
or tampering.
In this thesis, edible photonic microcavities are investigated as integrated platforms
for barcoding and sensing, operating above and below the lasing threshold. A systematic
investigation of consumable materials identifies naturally derived fluorophores, including
chlorophyll-A and vitamin B2, as a suitable gain medium for the realization of edible lasers.
These gain media are incorporated into edible resonators to design fully edible lasers in
various configurations. Edible microlasers based on whispering-gallery-mode (WGM) and
Fabry-Pérot (FP) cavity configurations are demonstrated. WGM microlasers are demonstrated
using doped liquid droplets of controlled sizes produced via microfluidic chips. In
addition, WGM microcavities operating below the lasing threshold are produced using solid
monodisperse silica microspheres coated with chlorophyll and silica via a modified Stöber
method. FP cavities are formed by confining the gain media between the mirrors based on
edible silver leaf. These microcavities exhibit ultra-narrow emission linewidths, enabling
high multiplexing capacity and sensitivity to surrounding changes such as refractive index.
When embedded directly into food products, they function as optical barcodes capable
of encoding tens of bits of data, such as manufacturer information and expiration dates,
while inherent fabrication variations provide physical unclonable functions (PUFs) for anticounterfeiting.
The strong environmental responsiveness of the WGM modes enables sensing
of key parameters relevant to food quality and safety, including sugar concentration,
pH, bacterial growth, and exposure to high temperatures.
However, practical limitations of liquid droplet-based microlasers operating above the
lasing threshold–such as the requirement for pulsed excitation, liquid droplet instability,
and limited fabrication scalability–make solid microcavities operating under continuous
wave (CW) excitation more suitable from a practical perspective. These solid microcavities
offer improved mechanical stability, as well as low-cost and scalable fabrication.
Importantly, the microlasers and microcavities developed in this study are entirely safe
for consumption, do not alter the appearance or taste of food, and are environmentally
friendly.
In summary, this work establishes a comprehensive framework for fully edible photonic
barcodes and sensors. The developed concepts extend beyond food and apply to pharmaceuticals,
cosmetics, agriculture, and other high-value consumable products, enabling new
strategies for secure authentication, traceability, and freshness monitoring directly within
the product itself.