Photoacoustic imaging provides high-resolution images at depths beyond the optical diffusion limit. To broaden its utility, there is need for molecular sensors capable of detecting environmental stimuli through alterations in photoacoustic signal. Photosynthetic organisms have evolved ingenious strategies to optimize light absorption through nanoscale ordered dye aggregation. Here, we use this concept to synthesize a stimuli-responsive nanoswitch with a large optical absorbance and sensing capabilities. Ordered dye aggregation between light-harvesting porphyrins was achieved through intercalation within thermoresponsive nanovesicles. This causes an absorbance red-shift of 74 nm and a 2.7-fold increase in absorptivity of the Qy-band, with concomitant changes in its photoacoustic spectrum. This spectral feature can be reversibly switched by exceeding a temperature threshold. Using this thermochromic property, we noninvasively determined a localized temperature change in vivo, relevant for monitoring thermal therapies of solid tumors. Similar strategies may be applied alongside photoacoustic imaging, to detect other stimuli such as pH and enzymatic activity.

Peptides can serve as versatile cancer-targeting ligands and have been used for clinically relevant applications such as cancer imaging and therapy. A current and long-standing focus within peptide research is the creation of structurally constrained peptides generated through cyclization. Cyclization is envisioned to enhance the selective binding, uptake, potency and stability of linear precursors. This review compares closely related linear and cyclic peptides in these respects. Peptide cyclization generally improves the selective binding and stability of linear precursors; however, not all cyclization strategies and constrained geometries enhance these properties to the same extent. In some instances, linear analogues actually have better cancer-targeting properties compared with their cyclic counterparts. Although cyclization does not necessarily improve the cancer-targeting properties of linear analogues, cyclic peptides may obtain properties that allow them to be used for additional applications. This review aims to convey the advantages and limitations of cyclic cancer-targeting peptides.

We demonstrate that porphyrins can be used as efficient cross-linkers to generate a new class of hydrogels with enabling optical properties. Tetracarboxylic acid porphyrins reacted with PEG diamines to form a condensation polyamide in a range of appropriate conditions, with respect to reaction time, diisopropylethylamine initiator concentration, porphyrin-to-PEG ratio, porphyrin concentration, and PEG size. The network structure of the hydrogel maintained a porphyrin spacing that prevented excessive fluorescence self-quenching despite high porphyrin density. The near-infrared properties readily enabled low background, noninvasive fluorescence monitoring of the implanted hydrogel in vivo, as well as its image-guided surgical removal in real time using a low-cost fluorescence camera prototype. Emission could be tuned by incorporating copper metalloporphyrins into the network. The approach of creating hydrogels using cross-linking porphyrin comonomers creates opportunities for new polymer designs with strong optical character.

Most animals store energy as long-chain triacylglycerols (lcTAGs). Trace amounts of acetylated triacylglycerols (acTAGs) have been reported in animals, but are not accumulated, likely because they have lower energy density than lcTAGs. Here we report that acTAGs comprise 36% of the neutral lipid pool of overwintering prepupae of the goldenrod gall fly, Eurosta solidaginis, while only 17% of the neutral lipid pool is made up of typical lcTAGs. These high concentrations of acTAGs, present only during winter, appear to be synthesized by E. solidaginis and are not found in other freezetolerant insects, nor in the plant host. The mixture of acTAGs found in E. solidaginis has a significantly lower melting point than equivalent lcTAGs, and thus remains liquid at temperatures at which E. solidaginis is frozen in the field, and depresses the melting point of aqueous solutions in a manner unusual for neutral lipids. We note that accumulation of acTAGs coincides with preparation for overwintering and the seasonal acquisition of freeze tolerance. This is the first observation of accumulation of acTAGs by an animal, and the first evidence of dynamic interconversion between acTAGs and lcTAGs during development and in response to stress. INTRODUCTIONLipids fulfill diverse biological functions including cell membrane structure, signalling and energy storage (Canavoso et al., 2001;Reue, 2011;Yen et al., 2008). Long-chain triacylglycerols (lcTAGs) are generally used as fuel stores by animals because of their high energy density, and are consequently the most abundant lipid class in animals (Williams et al., 2011;Yen et al., 2008). No other neutral lipid has been reported as a storage molecule in terrestrial animals.Instead of having three long-chain fatty esters (as in lcTAGs), acetylated triacylglycerols (acTAGs) have an acetyl group esterified at the 3-position of the glycerol backbone. This distinct structure results in the reduced viscosity and the significantly lower energy density of acTAGs compared with lcTAGs (Durrett et al., 2010). Trace amounts of acTAGs have been described in a broad range of organisms, including the antlers of Japanese deer (Cervus nippon) (Yang et al., 2004), the udders of domestic cows (Bos primigenius) (Limb et al., 1999) and the seeds of the burning bush plant (Euonymus alatus) (Durrett et al., 2010). acTAGs constitute a very small proportion of the total lipid pool in the two mammal species investigated [<0.1% by mass Limb et al., 1999;Yang et al., 2004)], but predominate (92% by moles) in E. alatus seed oils (Durrett et al., 2010). Euonymus alatus synthesises acTAGs via an unusual diacylglycerol acyltransferase (DGAT) by esterifying an acetyl group, rather than a third long-chain fatty acid, to diacylglycerol (DAG) (Durrett et al., 2010). Although trace acTAGs are present in a few animals, we are not aware of any clear hypotheses for a physiological role of acTAGs in biological systems. Here we report that the goldenrod gall fly, Eurosta solidaginis (Fitch 1855), accumulates significan...