*Article* **Surface Functionalisation of Self-Assembled Quantum Dot Microlasers with a DNA Aptamer**

**Bethan K. Charlton, Dillon H. Downie, Isaac Noman, Pedro Urbano Alves, Charlotte J. Eling and Nicolas Laurand \***

Technology & Innovation Centre, Institute of Photonics, University of Strathclyde, 99 George Street, Glasgow G1 1RD, UK; bethan.charlton@strath.ac.uk (B.K.C.); dillon.downie@strath.ac.uk (D.H.D.); isaac.noman@strath.ac.uk (I.N.); pedro.alves@strath.ac.uk (P.U.A.); charlotte.eling@strath.ac.uk (C.J.E.) **\*** Correspondence: nicolas.laurand@strath.ac.uk

**Abstract:** The surface functionalisation of self-assembled colloidal quantum dot supraparticle lasers with a thrombin binding aptamer (TBA-15) has been demonstrated. The self-assembly of CdSSe/ZnS alloyed core/shell microsphere-shape CQD supraparticles emitting at 630 nm was carried out using an oil-in-water emulsion technique, yielding microspheres with an oleic acid surface and an average diameter of 7.3 ± 5.3 μm. Surface modification of the microspheres was achieved through a ligand exchange with mercaptopropionic acid and the subsequent attachment of TBA-15 using EDC/NHS coupling, confirmed by zeta potential and Fourier transform IR spectroscopy. Lasing functionality between 627 nm and 635 nm was retained post-functionalisation, with oleic acid- and TBA-coated microspheres exhibiting laser oscillation with thresholds as low as 4.10 <sup>±</sup> 0.37 mJ·cm−<sup>2</sup> and 7.23 <sup>±</sup> 0.78 mJ·cm<sup>−</sup>2, respectively.

**Keywords:** colloidal quantum dots; microsphere lasers; whispering gallery mode laser; surface functionalisation; self-assembled supraparticles; aptamers
