This feature issue of Biomedical Optics Express presents studies which were the focus of the fourth OTA Topical Meeting that was held on 12-15 April 2015 in Vancouver, Canada.

In April this year, the OSA organized the fourth installment of the Optical Trapping and Applications (OTA) Topical Meeting as part of the Optics in the Life Sciences Congress in Vancouver, Canada. Over three full days of technical sessions, authors presented their groundbreaking research in a wide diversity of topics with the common theme of being related to optical trapping applications. The papers published in this issue of Biomedical Optics Express [1] are an assortment of the contributions from authors who presented their work at this past OTA meeting.

Included in this issue is a paper from Yoshio Tanaka and Shin-ichi Wakida which shows that a microlens array can be used to augment time-shared optical tweezers for dynamic microbead manipulation [2]. The system they employ uses a dual time shared scanning system laser system which the authors show is capable of creating dynamically alterable arrays of beads when combined with the microlens array. This result shows that although the system is less flexible than one using a Spatial Light Modulator (SLM) it is capable of creating large and complex patterns of beads at a lower expense. Also in this issue Craig McDonald and David McGloin show an ingenious use for bubble wrap as a vessel for culturing cells and performing optical tweezer experiments [3]. This work is innovative in two ways, not only do they perform the cell culture in the bubble wrap, demonstrating biophysical analysis in a common household material, but they also use a drop of PDMS to create a low-cost optical trapping system. In another contribution to this issue Alison Huff et al. study the trapping of particles whose refractive index is close to that of the medium they are suspended in [4]. They find that where the particles are stability or unstably trapped depends sensitively on the fiber separations and the size of the particles, information that will be of great use for the studies of soft matter stretching experiments that are regularly carried out with these dual fiber traps. E. Flores-Flores et al. have contributed a paper showing the trapping and manipulation of particles through laser-induced convection current and photophoresis [5]. They use a laser spot to heat up an amorphous silicon film creating convection currents in liquid centered above the illuminated area. This allows the manipulation of multiple particles at low laser powers (less than 1mW) however they also show that at higher powers (over 3mW) a thermo-photophoretic force dominates pushing the particles away from the illuminated/heated region. Dipankar Mondal and Debabrata Goswami’s paper shows how it is possible to measure the temperature at the trapping center by studying the dynamics of the trapped beads and that whilst doing so they can use a second laser at a more absorbing wavelength to change the temperature of the liquid [6]. This two wavelength approach then provides accurate control over the temperature in the water and the results are backed up by a geometric ray optics model. Finally, in a second paper to look at heating in an optical trap, Ana Andres-Arroyo et al. use dark field spectroscopy to study the heating that is present in metallic nanoparticles when optically trapped [7]. Some heating must exist due to the non-negligible extinction that these plasmonic particles exhibit and in this paper they show that the amount of heating can vary by a large degree which is attributed to variations in the axial position at which the particles are trapped.