A distributed feedback for organic semiconductor laser platform for assessing the risk of cardiovascular disease

Organic distributed feedback (DFB) lasers are a class of evanescent wave technology that can be used to measure changes in refractive index at the laser surface. These sensors are highly attractive for biosensing applications as they provide a sensitive platform for the label-free detection of a range of analytes, possibly in real-time, and they can be multiplexed for the detection of a suite of different analytes from a single test sample. The simple implementation of DFB lasers for sensing also means that they can be packaged into a compact sensing platform; this is especially true of DFB lasers incorporating an organic semiconductor as the gain layer where optical pumping may be performed with a compact source, such as a laser diode. In addition, organic semiconductor based DFB lasers have the potential for improved sensitivity relative to other organic DFB lasers (such as dye-doped) as the refractive index of organic semiconductors is generally higher, which leads to an increase in the interaction of the laser mode with the analyte binding region at the laser surface. In this thesis, the rst demonstration of an organic semiconductor (oligofluorene truxene (T3)) DFB laser for biosensing applications is described. Sensor development is focused on the ultimate aim of incorporating a T3 DFB laser into a compact and portable highthroughput sensing platform for the detection of cardiac biomarkers, Apolipoprotein B100, C-reactive protein and B-type natriuretic peptide in particular. Detection of these biomarkers is to be achieved via functionalisation of the T3 surface with oligonucleotide based probes. The structure of the T3 DFB laser is optimised experimentally and theoretically by tuning the gain layer thickness to maximise sensitivity to changes in refractive index at the laser surface, such as the binding of an analyte. The optimised laser sensor has a laser threshold of 30 µJ.cm⁻²/6 kW.cm⁻² (5 ns pulse duration) which makes optical pumping with a laser diode a possibility. The sensing potential of the DFB laser is shown via the detection of bulk solution refractive index changes and the addition of biomolecules to the laser surface, where a bulk sensitivity of 22 nm per refractive index unit is observed. The specific biosensing potential of the laser is highlighted through the functionalisation of the laser surface with biotin molecules and the subsequent detection of the complementary protein, avidin. The lowest limit of avidin detection achieved is 1µg.mL⁻¹; at this level of sensitivity, the current T3 laser is expected to be able to detect the larger and more abundant of two of the three cardiac biomarker targets, ApoB and CRP. The effects of structural changes to device sensitivity are modelled theoretically and demonstrate that detection of BNP may be achieved through the addition of a high-index cladding layer, a technique currently used for dye-doped DFB lasers. The first demonstration of a DFB laser used for reversible sensing is also presented in this thesis. Through the use of desthiobiotin, a biotin analogue, reversible avidin detection is performed. A reversible biosensor may be of particular interest for applications where a large number of repeated measurements are required, and may be prohibitive to the use of single-use, disposable sensors. Finally, functionalisation of the DFB laser with oligonucleotide probes is described. Several different techniques are explored for immobilisation of oligonucleotide probes on the T3 surface, with click chemistry and sulfhydryl linkage chemistries showing the most promise.Organic distributed feedback (DFB) lasers are a class of evanescent wave technology that can be used to measure changes in refractive index at the laser surface. These sensors are highly attractive for biosensing applications as they provide a sensitive platform for the label-free detection of a range of analytes, possibly in real-time, and they can be multiplexed for the detection of a suite of different analytes from a single test sample. The simple implementation of DFB lasers for sensing also means that they can be packaged into a compact sensing platform; this is especially true of DFB lasers incorporating an organic semiconductor as the gain layer where optical pumping may be performed with a compact source, such as a laser diode. In addition, organic semiconductor based DFB lasers have the potential for improved sensitivity relative to other organic DFB lasers (such as dye-doped) as the refractive index of organic semiconductors is generally higher, which leads to an increase in the interaction of the laser mode with the analyte binding region at the laser surface. In this thesis, the rst demonstration of an organic semiconductor (oligofluorene truxene (T3)) DFB laser for biosensing applications is described. Sensor development is focused on the ultimate aim of incorporating a T3 DFB laser into a compact and portable highthroughput sensing platform for the detection of cardiac biomarkers, Apolipoprotein B100, C-reactive protein and B-type natriuretic peptide in particular. Detection of these biomarkers is to be achieved via functionalisation of the T3 surface with oligonucleotide based probes. The structure of the T3 DFB laser is optimised experimentally and theoretically by tuning the gain layer thickness to maximise sensitivity to changes in refractive index at the laser surface, such as the binding of an analyte. The optimised laser sensor has a laser threshold of 30 µJ.cm⁻²/6 kW.cm⁻² (5 ns pulse duration) which makes optical pumping with a laser diode a possibility. The sensing potential of the DFB laser is shown via the detection of bulk solution refractive index changes and the addition of biomolecules to the laser surface, where a bulk sensitivity of 22 nm per refractive index unit is observed. The specific biosensing potential of the laser is highlighted through the functionalisation of the laser surface with biotin molecules and the subsequent detection of the complementary protein, avidin. The lowest limit of avidin detection achieved is 1µg.mL⁻¹; at this level of sensitivity, the current T3 laser is expected to be able to detect the larger and more abundant of two of the three cardiac biomarker targets, ApoB and CRP. The effects of structural changes to device sensitivity are modelled theoretically and demonstrate that detection of BNP may be achieved through the addition of a high-index cladding layer, a technique currently used for dye-doped DFB lasers. The first demonstration of a DFB laser used for reversible sensing is also presented in this thesis. Through the use of desthiobiotin, a biotin analogue, reversible avidin detection is performed. A reversible biosensor may be of particular interest for applications where a large number of repeated measurements are required, and may be prohibitive to the use of single-use, disposable sensors. Finally, functionalisation of the DFB laser with oligonucleotide probes is described. Several different techniques are explored for immobilisation of oligonucleotide probes on the T3 surface, with click chemistry and sulfhydryl linkage chemistries showing the most promise