Oligosaccharide Sensing Using Fluorophore-Probed Curdlans in Aqueous Media

Abstract

Saccharide sensing in aqueous media has recently garnered considerable attention in supramolecular and analytical chemistry; however, it still faces significant challenges. Herein, we report oligosaccharide sensing using the designed and synthesized fluorophore-probed curdlans. Aggregation-induced emission of the tetraphenylethylene (TPE) chromophore is a powerful candidate for outputting fluorescence signals upon the addition of the target oligosaccharide acarbose. Among the saccharides tested, the TPE-Cur chemosensors simultaneously exhibited high sensitivity and excellent selectivity toward acarbose. Morphological studies using atomic force microscopy, dynamic light scattering, fluorescence spectroscopy, and lifetime measurements revealed the importance of globule-to-coaggregation conversion upon oligosaccharide incorporation into the dynamic hydrogen-bonding networks of the curdlan string. This study provides perspectives for saccharide-responsive materials that are an attractive alternative to conventional chemosensors, which are difficult to sense in aqueous media.

Fluorophore-Probed Curdlan Polysaccharide Chemosensor: “Turn-On” Oligosaccharide Sensing in Aqueous Media

“…In Figure c, the titration data show a good straight line up to 100 μM and thereafter reach a plateau simply because of the solubility limitation of coaggregation. Thus, in the dynamic range, the slope was estimated as a sensitivity (Δ int = 7.38 [acarbose (μM)]); the sensitivity is slightly higher than that (−5.94) of the previous “turn-off” chemosensor ( TPE-Cur ) . Moreover, the LOD value was also estimated as 5 μM (see the data and LOD definition in Figure S6 in the SI), which is equal to that of TPE-Cur .…”

“…Thus, in the dynamic range, the slope was estimated as a sensitivity (Δ int = 7.38 [acarbose (μM)]); the sensitivity is slightly higher than that (−5.94) of the previous “turn-off” chemosensor ( TPE-Cur ) . Moreover, the LOD value was also estimated as 5 μM (see the data and LOD definition in Figure S6 in the SI), which is equal to that of TPE-Cur . It is noteworthy that Rhod-Cur enables ultrahigh detection of the medically useful acarbose with the lowest LOD based on the fluorescence “turn-on” behavior.…”

“…Morphological investigation studies on Por-Curs revealed that Cur-saccharide coaggregation induced by oligosaccharide insertion into the dynamic Cur string plays a significant role; the globule expands from its original state to that of the coaggregated form upon saccharide addition (Figure e). , Based on the globular expansion, we realized that CD and fluorescent reporters can be used to elucidate the structural (morphological) changes of modified Curs upon saccharide addition. Furthermore, aggregation-induced emission (AIE)-based tetraphenylethylene (TPE) was selected because it is the first fluorophore prototype for modified Cur. , We reported that the original globule of TPE-Cur initially emits strongly and its fluorescence intensity gradually decreases upon steady addition of saccharide, yielding an appreciable LOD of 5 μM . The decrease in fluorescence is consistent with the expansion of globular aggregates via globule-to-coaggregation conversion.…”

“…Furthermore, aggregation-induced emission (AIE)-based tetraphenylethylene (TPE) was selected because it is the first fluorophore prototype for modified Cur. 48 , 49 We reported that the original globule of TPE-Cur initially emits strongly and its fluorescence intensity gradually decreases upon steady addition of saccharide, yielding an appreciable LOD of 5 μM. 48 The decrease in fluorescence is consistent with the expansion of globular aggregates via globule-to-coaggregation conversion.…”

“… 48 , 49 We reported that the original globule of TPE-Cur initially emits strongly and its fluorescence intensity gradually decreases upon steady addition of saccharide, yielding an appreciable LOD of 5 μM. 48 The decrease in fluorescence is consistent with the expansion of globular aggregates via globule-to-coaggregation conversion. Therefore, this finding inspired us to investigate the possibility of a “turn-on” fluorescence reporter for smart Cur chemosensors.…”