Organic semiconductor lasers are a sensitive biosensing platform that respond to specific biomolecule binding events. So far, such biosensors have utilized protein-based interactions for surface functionalization but a nucleic acid-based strategy would considerably widen their utility as a general biodiagnostic platform. This manuscript reports two important advances for DNA-based sensing using an organic semiconductor (OS) distributed feedback (DFB) laser. First, the immobilization of alkyne-tagged 12/18-mer oligodeoxyribonucleotide (ODN) probes by Cu-catalyzed azide alkyne cycloaddition (CuAAC) or "click-chemistry" onto an 80 nm thick OS laser film modified with an azide-presenting polyelectrolyte monolayer is presented. Second, sequence-selective binding to these immobilized probes with complementary ODN-functionalized silver nanoparticles, is detected. As binding occurs, the nanoparticles increase the optical losses of the laser mode through plasmonic scattering and absorption, and this causes a rise in the threshold pump energy required for laser action that is proportional to the analyte concentration. By monitoring this threshold, detection of the complementary ODN target down to 11.5 pM is achieved. This complementary binding on the laser surface is independently confirmed through surface-enhanced Raman spectroscopy (SERS).

In this work, an organic composite polymer random laser (RL) operating underwater has been studied. The RL structure used in the test is a rod-shaped composite, formed by a mixture of an organic green light-emitting polymer and a UV transparent polymer matrix. RL action was sustained by both the multiple scattering and whispering-gallery-mode effect. The demonstration of RL action and the test of its operation lifetime in such an organic composite RL operating in water suggest the feasibility of its promising future applications in areas of underwater optical communications and/or remote optical sensing.

We present a truxene-based distributed feedback laser sensor and demonstrate its sensing capabilities. Results for bulk refractive index sensing, detection of nano-layer adsorption at the laser surface and specific biomolecule sensing are shown

Light-emitting polymers (LEPs) and related organic materials are attractive for many applications including optoelectronics and photonics [1]. They exhibit high photoluminescence quantum yields and can be tailored to emit at wavelengths across the whole visible spectrum. Furthermore, thanks to their 'soft matter' nature they offer great processing flexibility and should enable a wide range of novel devices and applications. Consequently, research into photonic components based on LEPs is being keenly pursued. However, organic materials typically suffer from photo-oxidation which can result in an alteration of the conjugation length at the molecular scale and ultimately destroys their light-emitting properties. Encapsulation of the LEPs while maintaining their processability and attractive physical properties is therefore essential to fully leverage this technology. The idea of composites, where a light-emitting material is blended in a protective host matrix, has often been the chosen strategy and many distributed feedback (DFB) lasers based on this approach were reported [2]. However, their laser oscillation threshold often exceeds the thresholds of their "neat" counterparts by more than 10 to 100-fold. In this work, we report a composite based on the incorporation of LEP into a novel polymer matrix which shows low amplified spontaneous emission (ASE) threshold. A mechanically-flexible, surfaceemitting DFB laser with a threshold as low as those typically shown by organic DFB lasers made from neat materials is also demonstrated.The LEP used in our experiments was a π-conjugated polymer based on a poly(p-phenylene vinylene)-core (PPV), called BBEHP-PPV [3]. Fig. 1 gives the absorption and emission spectrum of the polymer diluted in toluene. The polymer matrix is a blend of monomer and initiator which we will be calling here BAPO. It is in a chloroform solution for processing. The BBEHP-PPV powder was directly diluted in a volume of the BAPO solution to achieve the desired load and ultrasonically mixed for 3 minutes. The amplification capability of the composite was demonstrated by pulse-excitation (5 ns pulses / 10 Hz repetition rate) at 355 nm of a 25mg/mL nanocomposite film spin coated on silica. The ASE threshold was found to be 7.3kW/cm 2 (36.5µJ/cm 2 ) (Fig. 2) and the emission spectrum was seen to narrow above such fluence from 30nm down to 5nm. The surface emission DFB laser was realised by first reproducing by soft lithography a 340nm-period silica master grating in a fully transparent polymer, namely 1,4-cyclohexyldimethanol divinyl ether, using a transparency as substrate. A 20mg/mL-concentrated composite was then spin-coated onto the flexible reproduced grating for a targeted thickness below 200nm. Fig. 2 shows the threshold behaviour of the vertical emission of the laser. The laser emits at 522nm with a threshold below 2kW/cm 2 (<10 µJ/cm 2 ). Insets of Fig. 2 show a typical emission spectrum of the DFB laser, with a linewidth below 0.2nm limited by the resolution of our spectrometer, and a picture of ...