AIE-doped poly(ionic liquid) photonic spheres: a single sphere-based customizable sensing platform for the discrimination of multi-analytes

Based on one single AIE-doped photonic-structured polyionic liquid sphere, a novel customizable virtual sensor array system was developed.


General
Commercially available reagents and solvents were used as purchased from the chemical suppliers. Deionized water, 2-[4-(2-hydroxyethyl)-1-piperazinyl]ethanesulfonic acid buffer (HEPES, pH = 7.2) and human urine from volunteers were used for the preparation of target analyte solutions. 1 H and 13 C NMR spectra were recorded on a 400 MHz NMR spectrometer (JEOL, ECS-400). Electrospray ionization mass spectrometry (ESIMS) was measured on a mass spectrometer (Bruker, Esquire-LC). The fluorescence measurements of AIE activity were carried out using a fluorescence spectrometer (Perkin-Elmer, LS55). The optical images of spheres were recorded by an optical microscope (OLYMPUS, 51M) equipped with a CCD camera (OLYMPUS, UTV0.5XC-3). The fluorescence images of spheres were taken using an inverted fluorescence microscope (OLYMPUS, IX71; excitation filter 330-385 nm; long-pass emission > 420 nm) equipped with a CCD camera (OLYMPUS, DP73). The reflection spectra and emission spectra of spheres were measured by a microscope equipped with a fiber optic spectrometer (Ocean Optics, USB2000+). The size and structure of nanoparticles and spheres were characterized using scanning electron microscope (SEM) (Hitachi, SU8010). Energy-dispersive Xray spectroscopy (EDX) measurements were performed with the spectrometer attached on SEM system. The FTIR spectra of spheres were obtained with an attenuated total reflection IR spectroscopy (Bruker, VERTEX70). The PCA and cross-validated LDA (leave-one-out) were performed using Matlab software.
Synthesis of IL monomer. IL monomer was prepared according to reported procedures in literature. [  Synthesis of compound 2. Compound 1 was prepared according to reported procedures in literature. [3] A mixture of compound 3 (364.1 mg, 1 mmol), 1,3-dibromopropane (807.5 mg, 4 mmol) and potassium carbonate (1.105 g, 8 mmol) in acetone (20 mL) was refluxed for 12 hours under nitrogen. After cooling to room temperature, the solution was filtered, and the filtrate was evaporated under reduced pressure. The residue was dissolved in CH 2 Cl 2 and subjected to column chromatography with EA (ethyl acetate)/PE (petroleum ether, 60-90 o C) (v/v, 1/50) as eluent. Compound 2 was obtained as green oil (444.6 mg, 0.73 mmol) in 73.3% yield. 1

AIE activity of compound 3
The synthesized compound 3 here, an imidazolium-bearing tetraphenylethylene derivative, shows typical AIE activity in Figure S2 as reported for other tetraphenylethylene molecules. The solutions of compound 3 in good solvents such as CH 2 Cl 2 are almost non-emissive. The fluorescence of compound 5 can be turned on after aggregation induced by addition of poor solvents such as hexane into CH 2 Cl 2 . At 90 vol% hexane content, the fluorescence intensity is 53-fold higher than that of pure CH 2 Cl 2 solution, while the emission maximum is still located at 475 nm. Therefore, the synthesized compound 3 can be used as AIE luminogen.

Preparation of parent spheres
Parent AIE-doped PIL photonic spheres were prepared using an analogous method previously reported by our group. [4] These spheres were also fabricated by using a two-step method. First, monodisperse silica nanoparticles with a diameter of 170 nm self-assembled into ordered lattices by droplet-based microfluidics. Monodisperse silica particles with a diameter of ca. 170 nm were synthesized by the modified Stöber method. [5] Second, the solution containing 0.60 g ionic liquid monomer, 0.036 g crosslinker, 200 μL AIE luminogen stock methanol solution (3 mM) and 10 μL photoinitiator was infiltrated into the void spaces of the photonic spheres by capillary force. After polymerization under UV radiation followed by removal of silica template, the resultant parent spheres with highly ordered 3D inverse opal structure and doped AIE luminogen were fabricated.

Preparation of spheres of OHform
Counteranions of the parent spheres were completely converted from Brto OHby virtue of facile anion exchange according to a reported method in literature. [6] The above parent AIE-doped PIL photonic spheres were soaked in N 2 -saturated 1 M KOH aqueous solution for 24 h to convert the counteranions from the form of Brto OH -. This procedure was repeated three times to ensure thorough conversion of counteranions. Afterwards, the converted spheres were washed by N 2 -saturated deionized water until the pH of residual water was neutral. Thus, spheres of OHform for target multianalytes (amino acids and phosphate derivatives) were prepared. Remarkably, a very significant Bragg diffraction wavelength red-shift up to 157 nm was observed after the anion replacement, accompanying with a distinct color change of spheres from cyan to red by naked eye (Figure S5a). Energy-dispersive X-ray spectra further confirmed the complete conversion of Brto OHsince no Br could be detected after the anion conversion ( Figure S5b).

Spheres of OHform for the discrimination of 20 natural amino acids
AIE-doped PIL photonic spheres of OHform were incubated in 1 mL amino acid solutions for three days at room temperature under continuous stirring on an orbital shaker to achieve reaction equilibrium. Each sensing response to an analyte was measured with seven individual spheres to test reproducibility. Then the optical images, fluorescence images, reflection spectra and fluorescence spectra of spheres after binding with analytes were recorded. It should be noted that reflection spectra and emission spectra could be easily achieved on a microscope equipped with a fiber optic spectrometer in different detection modes. Bragg diffraction peak shifts (∆λ) were obtained by peak position before binding (λ 0 ) subtracting peak position after binding (λ 1 ): ∆λ = λ 0 -λ 1 . The folds of fluorescence enhancement ∆F/F 0 at 515 nm (or at 554 nm) were calculated by attaining fluorescence intensity before (F 0 ) and after (F 1 ) binding with amino acids at 515 nm (or at 554 nm): ∆F/F 0 = F 1 /F 0 -1. Then, the data was processed using PCA and LDA by Matlab.

Spheres of OHform for the discrimination of mixtures of amino acids
AIE-doped PIL photonic spheres of OHform were incubated in 1 mL mixtures of amino acids for three days at room temperature under continuous stirring on an orbital shaker to achieve reaction equilibrium. The concentration of individual amino acid in an arbitrary mixture was 10 mM.

Table S1
The identification of 15 blind samples which have been tested as training data sets before. S15 Part 3 Spheres of OHform for the discrimination of phosphate derivatives AIE-doped PIL photonic spheres of OHform were incubated in 1 mL phosphate derivative solutions for 6 hours at room temperature under continuous stirring on an orbital shaker to achieve reaction equilibrium. The concentration of phosphate derivatives was 10 μM.  The chiral spiral borate lithium was synthesized according to a reported method. [7] The parent AIEdoped PIL photonic spheres of Brform were soaked in 0.5 M chiral spiral borate lithium aqueous solution for 24 h to convert the counteranions from the form of Brto chiral spiral borate anion (CSBA). After this counteranion conversion, disappearance of Br peaks (11.6 wt%) at 1.340 and 1.480 keV, detection of B (8.0 wt%) at 0.183 keV, as well as typical adsorption bands of CSBA at 1720, 1494 and 694 cm -1 were observed, indicating the complete conversion of Brto CSBA. AIE-doped PIL photonic spheres of CSBA form were incubated in 1 mL chiral dicarboxylic acid solutions for 12 hours at room temperature under continuous stirring on an orbital shaker to achieve reaction equilibrium. The concentration of chiral dicarboxylic acids was 10 mM. S17 Part 5 customizable spheres of citrate form for the discrimination of metal ions The parent AIE-doped PIL photonic spheres of Brform were soaked in 1 M sodium citrate (CA) aqueous solution for 24 h to convert the counteranions from the form of Brto CA. After this counteranion conversion, 47 nm Bragg peak shift, disappearance of Br peaks (16.4 wt%) at 1.340 and 1.480 keV, typical adsorption band of CA at 1367 cm -1 were observed, indicating the complete conversion of Brto CA. AIE-doped PIL photonic spheres of citrate form were incubated in 1 mL metal ion solutions (pH = 5, 10 mM PBS buffer) for 1 hour at room temperature under continuous stirring on an orbital shaker to achieve reaction equilibrium. The concentration of metal ions was 100 μM. All ten metal ions (Al 3+ , Ba 2+ , Cd 2+ , Co 2+ , Cu 2+ , Hg 2+ , Ni 2+ , Pb 2+ , Sn 2+ , Zn 2+ ) were used in the form of chloride.