A wafer-scale ultrasensitive programmable chiroptical sensor

Abstract

Chiroptical enantioselective sensing is gaining traction across various applications. However, intrinsic molecular chiroptical responses are weak, and existing amplification approaches add synthesis, manufacturing, or operational complexity that limits sensitivity, scalability, and dynamic control. Here, we present a fundamentally new sensing paradigm merging adsorption-driven chirality induction with wafer-scale optical transduction in a programmable heterostructure containing twisted aligned carbon nanotubes (CNTs) and phase change materials (PCMs). Chiral molecules adsorb onto CNTs to form chiroptically active composites that are macroscopically assembled by alignment and rotational stacking, yielding large ultraviolet circular dichroism (CD). We resolve molecule concentration and handedness in a single device without lithography, hotspot delivery, or differential protocols, achieving sub-$μ$M sensitivity for CD-silent glucose and chiral amino acids enabled by $>10^5\,\mathrm{M^{-1}}$ adsorption constants. We validate adsorption using molecular dynamics simulations, reproduce experimental results using chiral transfer matrix simulations, and realize sensor programmability by tuning the PCM layer. This platform enables cost-effective in-situ enantiomer monitoring in aqueous environments.

Figures (5)

• Figure 1: Sensor architecture and characterization. (a) Schematic diagram of the sensor architecture consisting of multiple layers of twisted aligned CNTs, dielectrics, and tunable optical materials. (b) Normalized CD spectra of two-layer left-handed (L-twist, red line) and right-handed (R-twist, blue line) twisted aligned CNTs with a $40^{\circ}$ rotation angle between layers. (c) Schematic illustration of the apparatus for in situ characterizing sensors in aqueous solutions of chiral molecules. (d) Structural formula of D- and L-glucose molecules in water and its featureless CD spectrum.
• Figure 2: Enantioselective sensing of glucose enantiomers. Experimental CD spectra of the L-twist sensor in (a) the D-glucose solution and (b) the L-glucose solution with the glucose concentration from $0\,\upmu$M to $50\,\upmu$M (from black to cyan lines). (c) Experimental (dots) and fitting (dashed lines) enantioselective sensing curves of the L-twist sensor that quantifies the percentage change of the CD peak with respect to the concentrations of D- (red color) and L-glucose solutions (blue color). (d)--(f) Experimental CD spectra and the enantioselective sensing curves of the R-twist sensor in the same glucose concentration range. The line and dot styles are the same with (a)--(c).
• Figure 3: MD simulation. (a) Illustration of the MD simulation setup, including an achiral CNT surrounded by D-glucose and water molecules (not included for clarity). (b) Simulation (black dots) and fitting (red dashed line) number of adsorbed glucose molecules with respect to the total number of glucose molecules in the system.
• Figure 4: Optical simulation using chiral transfer matrix method. (a) Illustration of the adsorption of chiral molecules on a CNT, leading to a nonzero chirality parameter along the CNT axis. (b) Simulation CD spectra for the L-twist sensor in D- (dark to light red lines) and L-glucose solutions (dark to light blue lines), and corresponding experimental (dots) and simulation (lines) enantioselective sensing curves under various concentrations of D- (red color) and L-glucose (blue color) solutions from $0\,\upmu$M to $50\,\upmu$M. (c) Simulation CD spectra, and experimental and simulation enantioselective sensing curves for the R-twist sensor. The line and dot styles are the same as (b).
• Figure 5: Programmable sensor. (a) Schematic diagram of the programmable sensor by incorporating a GST film between twisted aligned CNTs. (b) Experimental (dots), fitting (dashed lines), and simulation (dotted lines) programmable sensing curves under amorphous (red color) and crystalline phases (blue color) of the GST, respectively.