Fluoride responsive single nanochannel: click fabrication and highly selective sensing in aqueous solution

A F– responsive nanochannel based on hydrogen-bonding interactions was designed to accomplish highly selective sensing in aqueous solution.


The synthesis of the C4CE
The synthesis of 1,3-dipropyl alkynyl-2,4-diester calix[4]arene (C4DE): 1, 3-dipropylalkynyl calix [4]arene (C4DY, 0.5 g, 0.69 mmol) was dissolved in dry THF (50 mL) and then NaH (0.66 g, 2.75 mmol) was added in batches. After stirring for 15 min, ethyl 2-bromoacetate (0.23 mL, 2.75 mmol) was added and the system was not stirred at room temperature until the raw material was run out of by the monitor of TLC for about 24 h. The product was obtained in white power through extraction and purified by ethyl acetate/ petroleum ether (v/v = 1:20) . The yield was 80%.
the system was not stirred at room temperature until the raw material was disappeared by the monitor of TLC for about 72 h.

Contact angles measurement
Contact angles were measured using an OCA20 (DataPhysics, Germany) contact-angle system at ambient temperature and saturated humidity. The original PI membrane for contact angle measurement was treated with NaClO (13% available chlorine) at 50 ℃for 60 min. And then The sample was removed from the etching solution and treated with the stopping solution (1 M KI) for 20 min. After that, the sample was treated with distilled water overnight. Just as the modification method in the inner wall of the nanochannel 3-azidopropan-1-amine (APAM) and 1, 3-dipropargylaza-p-tertbutylcalix[4]crown (C4CE) was modified on the surface of the film successively. Before the contact angle test, the sample was blown dry with N 2 . In each measurement, an about 1μL droplet of water was dispensed onto the surface of PI membrane.
The average contact angel value was obtained at five different positions of the same membrane. As shown in Figure S5, the change of the wettability of the surface means the change of the chemical composition , to some extent, which indicated the successful modification of the APAM and C4CE. S9 XPS X-ray photoelectron spectra (XPS) data were obtained with an ESCALab220i-XL electron spectrometer from VG Scientific using 300 W Al Kα radiation. In this work, to further prove the C4CE modified successfully by testing the nitrogen element, the PET film was used instead of the PI film. And also the COOwas exposed after etching of the PET film, that was the same with the PI film. All peaks were referenced to C 1s (CHx) at 284.8eV in the deconvoluted high resolution C 1s spectra. The nitrogen element existed in the PET film indicates that 3-azidopropan-1-amine (APAM) and 1, 3-dipropargylazap-tert-butylcalix[4]crown (C4CE) was modified on the surface of the film successfully.

Fig S7
XPS spectra of PET films before and after modification. The control was referenced to the original film (black) . The modified APAM was referenced to the film after the modification of APAM (red), and the modified C4CE was referenced to the film after the modification of C4CE (blue). The nitrogen element existed in the PET film indicates that APAM and C4CE was modified on the surface of the film successfully. S10 Table S1 the XPS data of the film before modification Table S2 the XPS data of the film after APAM modification Table S3 the XPS data of the film after C4CE modification S11

Laser scanning confocal microscopy
In order to directly characterize the Fcaptured in the conical nanochannel, the host C4CE was derived and the dansyl chloride (DNS) severed as the fluorophore was introduced. According to the method in the literature, the DNS-C4CE was synthesis as follows: 1 mL of C4CE (1mM) in acetonitrile, 1 mL of DNS (2mM) in acetone and 2 mL of the buffer solution of sodium bicarbonate (NaHCO 3 ) at pH = 10.5 was added in flask. Subsequently, the flask was protected from the light for 1h.
Fluorescence microscopic images were acquired by using a Zeiss confocal laser scanning unit mounted on a LSM710 fixedstage upright microscope. In this experiment, the etched porous PI film was modified with the DNS-C4CE according to the same method in the single nanochannel. And then the DNS-C4CE -modified porous PI film was immersed in 10 -3 M Fsolution for 3 h. Before the measurement, the film was washed by distilled water.

Scheme 2
The synthesis of DNS-C4CE with the fluorophore of dansyl chloride (DNS). the ratio of negative to positive current at -2 V), and K is the binding strength constant, was found to provide a perfect fit to the experimental data. Therefore, according to the date from Figure S8, C/R -/+ was calculated and then the relation of C/R -/+ -C was linear fit.

The I-V curve for selectivity in original channel and APAM channel
All of the regression values (r 2 ) were above 0.9996. This different linears indicated the C4CE channel exhibited selectivity for Fin quality.

The anti-interference performance
(1) the interference from the other anions In this anti-interference test, the concentration of interfering ions added was 10 -3 M and the concentration of determined Fwas 10 -5 M. The individual interference ion and mixed interference ions was added and determined respectively. In Table 2, the Ratio denotes the relative ratio of the current change at -2 V and the expression was (I-I 0 ) / I 0 , where I 0 was the current at -2 V in absence of the analytical ions and I was the current at -2 V in presence of the analytical ions. Ratio 0 was the value for Fdetermination without interference ions and Ratio 1 was the value for Fdetermination with interference ion. The recovery was calculated by the ratio of Ratio 1 and Ratio 0 to estimate the anti-interference performance. 10 -3 10 -3 10 -3 10 -3 10 -3 10 -3 10 -3 10 -3 10 -3 10 -5 10 -5 10 -5 10 -5 10 -5 10 -5 10 -5 10 -5 10 -5 (2) the interference from the serum