There are millions of avoidable injuries and deaths across the globe due to chemical

exposure in industries such as transportation, utilities, farming and manufacturing

every year. We must strive to find ways of alleviating this plight on members of our

global community. Sensing harmful chemicals is often costly, complicated, and

cumbersome, though it is paramount that we have effective monitoring, so to achieve

this, we explore the possibility of a portable, easy-to-use, colorimetric device, that

allows clear and obvious detection of harmful substances.

Within the introduction to this thesis, colorimetric sensors were examined, specifically

photonic crystals (PCs), and their physical principles. Exploration was undertaken of

how the interesting and novel functionalities of a 2D nanomaterial, molybdenum

disulphide (MoS2), could enhance PCs and explore possible exfoliation route, liquid-

phase exfoliation (LPE), as a low-cost and scalable approach.

Within this work, I use spectroscopic ellipsometry (SE) to probe the optical constants

of thin films of LPE MoS2. After developing a modelling protocol to fit spectroscopic

data, I successfully compared our methods to data reported in literature using

mechanically exfoliated samples. From this, I pushed the capabilities of SE and

described the optical constants of vacuum filtered and spray deposited films of LPE

MoS2, something which has not been achieved in the literature so far. I then went

further, exposing spray deposited LPE MoS2 films to chemicals of industrial relevance.

Through SE, I measured increases and decreases in MoS2 optical constants,

depending on whether the analyte was of an electron accepting and donating nature,

respectively. Alongside these experiments, I successfully adapted a method of PC

fabrication, evaporation driven self-assembly, of polymeric nanospheres to produce

robust, free-standing crystals. The adaptation described here allowed us to embed

LPE MoS2, locking the nanomaterial within interstitial sites of our PCs, to produce

phenomenal increases in the structural colour of the crystals. After refining this

method, through changing our bespoke latex to a commercially available one with a

suitable particle size, I solved issues related to the creation of thin film crystals, which

are better suited to spectrophotometric analysis. This set the stage to be able to

monitor the PC stopband (SB) through quantitative spectrophotometric analysis of thin

crystals and, in parallel, carry out qualitative observation of structural colour changes

with the inclusion of MoS2 or the exposure to chemical analytes.

This platform was then used to perform sensing experiments, whereby thin and thick

crystals containing different loadings of MoS2 were exposed to various concentrations

of electron accepting/donating analytes. Observed within this thesis is the red- and

blue-shifting of the SB and visual colour of PCs, due to these respective chemicals.

Possible mechanisms which lead to this interesting interaction were then described.

Within the final experimental chapter, the ability for PC crystals to be used in real-

world scenarios was showcased, by undertaking cell culture experiments upon their

surface which showed total biocompatibility with mammalian cells. This could act as a

model for exposure to skin cells in a wearable device or give a foundation for future

works which push the technology into the biomedical field as a biosensor.

This work showcases several groundbreaking achievements in the realm of chemical

sensing via polymeric PCs and nanomaterials. It pushes the envelope for possibilities

of SE through the use of this apparatus in optical characterisation and sensing

capabilities of LPE MoS2. Altogether, this thesis shows the ability of a novel system to

help combat a global issue, inherent to many sectors, and potentially allows us to

further this technology to ultimately save lives and prevent tragedy by allowing robust,

simple, and clear, colorimetric chemical detection.