Control over the emerging chirality in supramolecular gels and solutions by chiral microvortices in milliseconds

The origin of homochirality in life is a fundamental mystery. Symmetry breaking and subsequent amplification of chiral bias are regarded as one of the underlying mechanisms. However, the selection and control of initial chiral bias in a spontaneous mirror symmetry breaking process remains a great challenge. Here we show experimental evidences that laminar chiral microvortices generated within asymmetric microchambers can lead to a hydrodynamic selection of initial chiral bias of supramolecular systems composed of exclusively achiral molecules within milliseconds. The self-assembled nuclei with the chirality sign affected by the shear force of enantiomorphic microvortices are subsequently amplified into almost absolutely chirality-controlled supramolecular gels or nanotubes. In contrast, turbulent vortices in stirring cuvettes fail to select the chirality of supramolecular gels. This study reveals that a laminar chiral microflow can induce enantioselection far from equilibrium, and provides an insight on the origin of natural homochirality.

stirring at 900 rpm. BTAC gels rapidly form when the volume ratio of H 2 O to DMF is near 2:5. The average volume of water drops is 20 μL and the DMF volume is 1000 μL.

Supplementary Methods
Master mold fabrication The master molds for the inclined microchannels were manufactured using T3050 photoresist (Baisiyou, China) by MiTASChip (China). A 4 inch silicon wafer was baked at 150 C for 5 min and left still for 5 min. The T3050 photoresist was spin-coated on the 4 inch wafer at 800 rpm for 35 sec under a vacuumed condition to obtain the desired thickness of ~50 μm. The coated wafer was left still for 2 min to even the surface. The photoresist was exposed to ultraviolet (UV) light for 15 sec through a photomask containing the microchannel patterns (Supplementary Figure 1).
The gap between photomask and photoresist was ~80 μm during the exposure. Before and after the exposure, the wafer was baked at: 60 C for 2 min, 95 C for 10 min, and 60 C for 2 min. The wafer was then soaked in a SU-8 developer (MicroChem, USA) to wash away the unexposed photoresist and finally baked at 150 C for 20 min.

Microchannel fabrication
The degassed mixture of PDMS and curing agent (10:1) was cast over the mold and then solidified at 80 °C for 20 min in an oven. After peeling off the PDMS slab from the silicon mold, the inlet and outlet ports were punched through the PDMS using a sharpened 19G dispensing needle (ID 0.75 mm, OD 1 mm). The PDMS was then treated with plasma (at ~55 Pa for 40 sec) and bonded to a glass substrate.
Plastic tubes were inserted into the inlet and outlet ports and glued with the adhesive sealant (Dow Corning 3145 RTV, USA).

Optimization of temperature and BTAC concentration
For temperature optimization, the microfluidic device was immersed into a water bath at different temperatures of 28 °C , 40 °C, and 50 °C during the self-assembly process (Supplementary Figure 4). The BTAC concentration in the middle infusion was kept at 61 mg mL -1 , leading to an average S18 concentration of ~ 1 mg mL -1 at the outlets under the flow conditions of 30-1-30 mL h -1 .
The CD spectra showed a negative Cotton effect for the L-outlet and a positive Cotton effect for the R-outlet only at 40 °C , whereas no opposite CD signals for the opposing outlets were detected at 28 °C and 50 °C.
For optimization of BTAC concentration, two additional BTAC concentrations, 30.5 and 91.5 mg mL -1 , were used while keeping the temperature at 40 °C (Supplementary Figure 5). No gels were formed and no CD signals were detected for 30.5 mg mL -1 BTAC. Using 91.5 mg mL -1 BTAC, gels were obtained, but no opposite CD signals were observed for the opposing outlets. Therefore, the BTAC concentration of 61 mg mL -1 and water batch temperature of 40 °C were used for microfluidic selfassembly of BTAC gels.

Spectra measurement
The CD and UV-Vis spectra of BTAC assemblies (270 nm to 500 nm) and TPPS 4 assemblies (400 nm to 520 nm) were measured using a JASCO J-1500 spectrometer (Japan). BTAC measurements were performed in a 0.1 mm cuvette using integrations of 1 s, data pitch of 0.5 nm, scanning speed of 500 nm min -1 , and single S19 acquisition with a bandwidth of 5 nm. DMF/H 2 O (v/v, 5/2) was used for the baseline correction. TPPS 4 measurements were performed in a quartz cuvette with a path length of 3 mm using integrations of 0.5 s, data pitch of 0.5 nm, scanning speed of 200 nm min -1 , and single acquisition with a bandwidth of 2 nm. A 1:61 dilution of the initial mixture solution (0.4 M C 2 mimBF 4 + 1.5 M HCl) was used for base line correction. The sign and magnitude of CD signal for TPPS 4 assemblies were determined as CD 493.5nm -CD 489.5nm .

Scanning electron microscopy (SEM)
The SEM characterizations of microchannel structure and BTAC gels were performed on a Hitachi S-4800 FE-SEM (Japan) with an accelerating voltage of 5 kV. Before SEM measurement, the samples on silicon wafers were dried in a vacuumed condition and then coated with a 5 nm Au layer for 30 s to increase the contrast.

Atomic force microscopy (AFM) Fresh mica substrate was pretreated using 100 mM
NiCl 2 solution for 5 min to facilitate the deposition of the TPPS 4 assemblies. A drop of solution containing TPPS 4 assemblies was then added onto the mica surface and kept still for 5 min to deposit these TPPS 4 assemblies. All the AFM images were taken in air using a MultiMode 8 AFM (Bruker, Germany) in the ScanAsyst mode with SNL-10 tips (Bruker, Germany) and analyzed by NanoScope Analysis software (Bruker, Germany).

Trajectory of a single microsphere in inclined microchamber
To track the motion of a single tracer particle in the inclined microchamber, we used a diluted particle suspension Residence time within inclined microchannel. The residence times of particles in inclined microchambers were determined by the Lagrangian particle tracking of tracer particles using the CFD software Fluent 6.4 (Ansys Inc., USA). The steady flow field without tracer particles was first obtained by solving the Navier-Stokes equations. The tracer particles (1 μm in diameter) were then spiked from the right upstream of the microchambers and their motions were predicted by integrating the force balance of the particle based on a Lagrangian formulation: where u is the flow velocity vector, V p the particle velocity vector, ρ p the particle density, C D the drag coefficient, Re s the relative Reynolds number sp Re a   uV , and g the S21 gravitational acceleration 1 . On the right hand of the force balance equation, the first term is the viscous drag force per unit particle mass, the second term is buoyant force that can be neglected for neutrally-buoyant particles, and the third term is the virtual mass force arising from the acceleration of the fluid around the particle. The residence time for a tracer particle was determined as the time interval between its entrance and exit of the microchamber. The average residence time for the spiked tracer particles (87 counts) was 36 ms with a maximal value of 100 ms. Calculation of the shear force The hydrodynamic torque to twist the nuclei was originated from the shear force. For a TPPS 4 /BTAC nucleus with a length of L S22 suspending in a flow field with a shear rate gradient Γ , the shear force exerting on the nucleus was estimated as s

Calculation of assembly time
A is the surface area of the nuclei determined as 1.5×10 -13 m 2 for BTAC fiber and 1.1×10 -14 m 2 for TPPS 4 tube. The Γ increased with off-wall distance and reached the maximum of 8×10 10 m -1 s -1 at the half height of the microchamber, where the maximum F s was estimated as 1.6 pN for BTAC nuclei and 0.1 pN for TPPS 4 nuclei. x