Although it may seem identical, your reflection in the mirror is actually a reversed, non-superimposable image; it's not the same as you. Similarly, in chemistry, mirror images of molecules (known as enantiomers) possess the same atoms and bonds, yet their spatial arrangements, interactions, and behaviours are fundamentally different.
For instance, in pharmacological applications such as drug delivery, these mirrored molecules can exhibit opposing behaviours with some potentially causing side effects, pointed out Chong Pei Ho, a Senior Scientist at A*STAR’s Institute of Microelectronics (IME). Adding to the complexity, a single molecule can be reflected in multiple ways, resulting in different mirror images.
Unsurprisingly, differentiating chiral mixtures at various concentrations and enantiomeric ratios has been an ongoing challenge in the field. A common method employed is vibrational circular dichroism (VCD) spectroscopy, a technique capable of distinguishing molecular chirality by using circularly-polarised light.
However, the method's sensitivity is limited due to the weak signals arising from the subtle interactions between the chemicals and the incoming light.
In a collaborative effort with researchers from the National University of Singapore, Ho and colleagues harnessed the properties of infrared chiral plasmonic metamaterials (IRCPMs) with the goal of intensifying VCD signals.
The researchers refined their metamaterial's design using temporal coupled-mode theory (TCMT). This allowed them to precisely adjust the disparity in thickness and the spatial relationship between adjacent nanorods, thereby amplifying the intensity of the light in the vicinity of the metamaterial's surface, while simultaneously curbing losses.
“The chiral molecules are exposed to the enhanced field, and will experience larger interactions,” explained Ho. Through this approach, the typically weak molecular signals from the VCD method were significantly amplified, pushing beyond previous constraints.
The research team's use of this innovative metamaterial led to a six-fold leap in VCD detection capabilities, distinguishing between molecules of differing chirality with unprecedented clarity compared to traditional methods. Their novel platform was also reported to pinpoint complex chiral protein structures at the zeptomole scale, aligning closely with the limit of current detection technologies.
Ho is enthusiastic about the potential impacts of their achievements, envisaging it as a cornerstone for the creation of highly efficient chiral sensors. The team is already considering the use of readily available materials, aiming for a seamless integration with standard wafer fabrication processes to upscale production.
The A*STAR-affiliated researchers contributing to this research are from the Institute of Microelectronics (IME).
