A Sensitive Pyrimethanil Sensor Based on Electrospun TiC/C Film

sensors Article A Sensitive Pyrimethanil Sensor Based on Electrospun Film Lg Sui, Tgtg Wu, Lijuan Liu, Honghong Wang, Qgqg Wang, Haoqg Hou Qiaohui Guo * Department Chemistry Chemical Engeerg, Jiangxi Normal University, Nanchang 330022, Cha; 15079058173@163.com (L.S.); wtt1874983756@163.com (T.W.); 15979385750@163.com (L.L.); WHHong816@163.com (H.W.); Wyuan0816@yeah.net (Q.W.); zxp1014@126.com (H.H.) * Correspondence: guoqiaohui@jxnu.edu.cn; Tel.: +86-791-8812-0389; Fax: +86-791-8812-0536 Received: 24 February 2019; Accepted: 26 March 2019; Published: 29 March 2019 Abstract: Titanium carbide (TiC) is a very significant transition metal carbide that displays excellent stability electrical conductivity. electrocatalytic activity TiC is similar to noble metals but is much less expensive. Here, carbon nanibers (CNFs)-supported TiC nanoparticles (NPs) film () is prepared by electrospng carbormal processes. Well-dispersed TiC NPs are embedded tightly to CNFs frameworks. electrochemical oxidation pyrimethanil (PMT) at -modified electrode displays enhanced redox properties, electrode surface is controlled simultaneously both by diffusion adsorption processes. When is applied for PMT determation, as-fabricated sensor shows good sensg performance, displayg a wide lear range (0.1 600 µm, R 2 = 0.998), low detection limit (33 nm, S/N = 3), good reproducibility with satisfied anti-terference ability. In addition, shows long-term stability good application natural samples. facile syntic method with good sensg performance makes promisg as novel electrode materials to fabricate efficient sensors. Keywords: electrospng; TiC; pyrimethanil; electrochemical sensor 1. Introduction To control plant pests or diseases, usage pesticides is widely relied upon [1]. Some se pesticides are used for protectg food crops durg cultivation post-harvest storage. However, most se chemicals may exist environment after ir usage [2]. refore, residues se pesticides would be discovered fruits, vegetables, or water, which threaten human health. As one kd anile epyrimide fungicides, pyrimethanil (PMT, chemical structure shown Scheme 1) plays a crucial role agriculture, as it is applied to control leaf scab some post-harvest diseases [3]. However, wide usage PMT would produce residues that may become a possible threat for health environment. Due to toxicity PMT, European Union Directive on drkg water quality established a maximum allowed concentration (0.1 µg/l) for PMT [4]. refore, developg a sensitive method to determe PMT is very important. Recently, PMT residues are monitored commonly by gas chromatography or high-performance liquid chromatography (HPLC) coupled with selective detectors [5 8]. se technologies display satisfactory accuracy, high reproducibility reliability, but y are also subject to some evitable shortcomgs, such as need for traed personnel, expensive struments, complex extraction steps. On or h, electrochemical methods have attracted much attention for quantitative analysis pesticide residues due to ir good stability, high sensitivity, low cost [9 11]. Sensors 2019, 19, 1531; doi:10.3390/s19071531 www.mdpi.com/journal/sensors

Sensors 2019, 19, 1531 2 10 Sensors 2019, 19, x FOR PEER REVIEW 2 10 Scheme 1. 1. chemical structure pyrimethanil (PMT). Recently, transition metal metal carbides, carbides, such such as TaC, as TaC, TiC, TiC, Mo 2 C, have Mo2C, attracted have attracted growg attention growg attention due to ir due high to ir catalytic high catalytic activity. activity. Additionally, Additionally, catalytic catalytic activity activity se transition se transition metal metal carbides carbides is similar is similar to that to that noble noble metals, metals, but but y y are are less less expensive. expensive. Particularly, as as a vital transition metal carbide, TiC displays wide applications supercapacitors [12], dye-sensitized solar cells [13], lithium-ion batteries [14], owg to its good chemical rmal stability, high catalytic activity, low conductivity (6.8 (6.8 10 10 5 Ω/cm). 5 Ω/cm). Recently, Recently, various various TiC nanostructures, TiC nanostructures, such as such core shell as core shell [12,15], [12,15], nanowire nanowire [14], nanorod [14], nanorod [16], [16], nanoparticle nanoparticle (NP) [17,18], (NP) [17,18], have been have widely been widely exploited. exploited. Although Although TiC NPs TiCcan NPseffectively can effectively improve improve its its electrochemical electrochemical activity, activity, y ytend tend to agglomerate, decreasg its specific surface area. Here, a hybrid TiC NPs loaded carbon nanibers () synsized via a simple electrospng carbormal approach. approach. Well-dispersed Well-dispersed NPs NPs were dispersed were dispersed tightly on tightly skeleton skeleton carbon nanibers carbon nanibers (CNFs). As(CNFs). expected, As expected, hybrid displayed hybrid superior displayed sensg superior performance sensg performance PMT determation. for PMT determation. In addition, In addition, also used for also detection used for PMT detection natural samples. PMT natural samples. 2. Experimental 2. 2.1. Experimental Reagents 2.1. Reagents Titanium tetrachloride (TiCl 4 ), polyacrylonitrile (PAN), polyvylpyrrolidone (PVP, M w = 1,500,000) were obtaed from Sigma-Aldrich. PMT purchased from Bepharm Co. Ltd. Titanium tetrachloride (TiCl4), polyacrylonitrile (PAN), polyvylpyrrolidone (PVP, Mw = (Guangzhou, Cha). Phosphate buffer sale (PBS) prepared by mixg 0.1 M NaH 2 PO 4 1,500,000) were obtaed from Sigma-Aldrich. PMT purchased from Bepharm Co. Ltd. Na 2 HPO 4. All solutions were dissolved with deionized water, obtaed from a Milli-Q water (Guangzhou, Cha). Phosphate buffer sale (PBS) prepared by mixg 0.1 M NaH2PO4 purifyg system (18 MΩ cm 1 ). water samples were obtaed from a stream Nanchang City Na2HPO4. All solutions were dissolved with deionized water, obtaed from a Milli-Q water (Jiangxi, Cha) filtered with 0.50 µm nylon. Two kds food (apple cucumber) were purifyg system (18 MΩ cm 1 ). water samples were obtaed from a stream Nanchang City obtaed from local supermarket. A part apple cucumber pericarp cut up added to (Jiangxi, Cha) filtered with 0.50 μm nylon. Two kds food (apple cucumber) were beaker, some ethanol added to dissolve pesticide residues. Assistg ultrasonic treatment obtaed from local supermarket. A part apple cucumber pericarp cut up added to conducted for about 60 m, n solution filtrated for furr experiments. beaker, some ethanol added to dissolve pesticide residues. Assistg ultrasonic treatment 2.2. Apparatus conducted for about 60 m, n solution filtrated for furr experiments. 2.2. Apparatus ATESCAN VEGA-3 scanng electron microscope (SEM) a Tecnai G20 transmission electron microscope (TEM) were used to characterize morphology. Raman spectroscopy (WITec-CRM200 ATESCAN VEGA-3 Raman system scanng wilectron a laser wavelength microscope (SEM) 532 nm) a Tecnai used tog20 characterize transmission electron microstructure microscope. (TEM) rmogravimetric were used to characterize analysis (TGA) morphology performed. onraman a SDT Q700 spectroscopy rmal (WITec-CRM200 analyzer (TA Instruments Raman system Co., Tokyo, with Japan) a laser under wavelength air atmosphere. 532 nm) Electrochemical used to experiments characterize were microstructure tested on CHI 760. E electrochemical rmogravimetric workstation analysis (Shanghai, (TGA) Cha). performed A three-electrode on a SDT Q700 configuration rmal analyzer employed (TA Instruments to performed Co., electrochemical Tokyo, Japan) experiments, under air atmosphere. which aelectrochemical platum wire experiments used for were auxiliary tested on CHI 760 reference E electrochemical electrode workstation Ag/AgCl (saturated (Shanghai, KCl), Cha). A bare three-electrode glass carbon configuration electrode (GC) employed used workg to performed electrochemical Electrochemical experiments, impedance spectroscopy which a platum (EIS) wire measured used for 0.1 auxiliary M KCl solution contag reference 5 mmelectrode Fe(CN) 3 /4 Ag/AgCl (saturated KCl), bare 6 (1:1). frequency 1.0 10 2 ~ 1.0 glass 10 carbon 5 Hz. electrode (GC) used as workg Electrochemical impedance spectroscopy (EIS) measured 0.1 M KCl solution contag 5 mm Fe(CN)6 3 /4 (1:1). frequency 2.3. Preparation 1.0 10 2 ~ 1.0 10 5 Hz. hybrid synsized by combation electrospng carbormal processes [19]. 2.3. Preparation Briefly, TiCl 4 (12 wt% relative to TiCl 4 ) dissolved PVP (TiCl 4 /PVP). PAN (18 wt% relative to PAN) dissolved hybrid DMAC synsized (PAN/DMAC), by combation n PAN/DMAC electrospng solution carbormal mixed with TiCl processes 4 /PVP [19]. Briefly, TiCl4 (12 wt% relative to TiCl4) dissolved PVP (TiCl4/PVP). PAN (18 wt% relative to PAN) dissolved DMAC (PAN/DMAC), n PAN/DMAC solution mixed with

Sensors 2019, 19, 1531 3 10 (1:1) solution with contuous strg for 4 h at 60 C. electrospng process under a 30 kv voltage, nanibers were collected onto a rotatg drum. as-electrospun nanibers (2 C/m, 5 h, air atmosphere), furr rmal treatment at 1000 C were oxidized at 230 Sensors 2019, 19, x FOR PEERCREVIEW 3 10 (10 C/m, 1 h, vacuum). For a comparison, CNFs film ( electrospng solution PAN/DMAC TiCl 4/PVP solution with contuous strg h at 60 C. electrospng process without (1:1) addition TiCl solution) for also4prepared under same condition. 4 /PVP under a 30 kv voltage, nanibers were collected onto a rotatg drum. as-electrospun 2.4. Electrode Preparation nanibers were oxidized at 230 C (2 C/m, 5 h, air atmosphere), furr rmal treatment at 1000 Glass C (10carbon C/m, 1 h, vacuum). a comparison, CNFs film usg ( electrospng electrode (GC, θ =For 3 mm) polished carefully Al2 O3 powder. solution electrode PAN/DMAC twice addition TiCl4water /PVP solution) also experiments. prepared under same rsed without sonicated with distilled used for furr An amount condition. 8 mg/ml dispersed a solvent mixture contag 25 µl Nafion (5 wt%) 250 µl distilled water by sonication. Immediately after dispersion, 6 µl slurry coated onto 2.4. GC Electrode electrodepreparation surface (/GC). 0.1 M PBS solution prepared by purgg with high purity nitrogen m a(gc, N2 blanket above solution durg Glass(Ncarbon Ɵ = 3 mm)mataed polished carefully usg Al2O3measurement. powder. 2 ) for 30electrode electrode rsed sonicated twice with distilled water used for furr experiments. An 3. Results Discussion amount 8 mg/ml dispersed a solvent mixture contag 25 μl Nafion (5 wt%) 250 μl distilled water by sonication. Immediately after dispersion, 6 μl slurry 3.1. Characterization coated onto GC electrode surface (/GC). 0.1 M PBS solution prepared by purgg with from PAN/TiCl4 nanibers. Durgabove carbormal high purity hybrid nitrogen (Nsynsized 2) for 30 m a N2 blanket mataed solutionprocess, durg nanibers were carbonized to CNFs, TiC NPs were formed situ. refore, hybrid measurement. corporated to one step. It can be seen from 1A that revealed 3D network structure, TiC NPs homogeneously dispersed on surface CNFs. detailed morphology 3. Results were Discussion furr performed by TEM technique. results showed that NPs were embedded to CNF frameworks ( 1B). 3.1. Characterization 1. SEM (A)(A) TEM ; Inset Inset SEM image CNFs. 1. SEM TEM(B) (B)images images ; SEM image CNFs. electrical evaluated via a Durg four-pot method usg hybrid conductivity synsized fromfilm PAN/TiCl 4 nanibers. probe carbormal process, followg equation nanibers were[19]: carbonized to CNFs, TiC NPs were formed situ. refore, L hybrid corporated to one step. It can σ =be seen from 1A that revealed 3D (1) RA network structure, TiC NPs were homogeneously dispersed on surface CNFs. where L morphology is distance twurr electrode (cm), R by is resistance film (Ω), that A is detailed between performed TEM technique. results showed 2 ). electrical conductivity CNFs 0.50 S cm 1. cross-sectional area film (cm NPs were embedded to CNF frameworks ( 1B). 1. results revealed that TiC However, electrical conductivity to 25.5via S cm electrical conductivity film creased evaluated a four-pot probe method usg NPs embedded CNFs could enhance percolation-type conduction [20]. followg equation [19]: σ= L RA (1) where L is distance between two electrode (cm), R is resistance film (Ω), A is cross-sectional area film (cm2). electrical conductivity CNFs 0.50 S cm 1. However, electrical conductivity creased to 25.5 S cm 1. results revealed that TiC

Sensors 2019, 19, 1531 4 10 Raman spectroscopy is widely used to vestigate structure molecule crystal lattice. re were two strong peaks centered at 1338 1575 cm 1, which were graphite peaks, or peaks at 264, 416, 602 cm 1 corresponded to TiC phase (JCPDS: 65 0242) ( 2A), confirmg formation TiC nanocrystal. TGA analysis used to measure rmal stability. As shown 2B, a weight crease (250 550 C) obtaed from. Sensors 2019, 19, x FOR PEER REVIEW 4 10 crease weight due to TiC oxidation to titanium dioxide (TiO2 ) air atmosphere (TiC + 2O2 TiO2 + CO2 ) [19]. amount TiC 40.3%, accordg to change weight [21]. Sensors 2019, 19, x FORtemperature PEER REVIEW 5% weight loss 550 C, which higher than 4that 10 Additionally, CNFs (390 C), demonstratg that owned much better rmal stability. 2. Raman spectra (A) TGA curves (B) CNF air atmosphere. Raman spectroscopy is widely used tocurves vestigate structure molecule crystal lattice. 2. Raman spectra TGA curves(b) (B) atmosphere. 2. Raman spectra (A)(A) TGA CNF CNF airair atmosphere. re were two strong peaks centered at 1338 1575 cm 1, which were graphite peaks 3.2. Electrochemical Behavior, spectroscopy or peaks is at widely 264, 416, to602 cm 1 corresponded to molecule TiC phase Raman used vestigate structure (JCPDS: crystal 65 0242) lattice. ( 2A), confirmg formation TiC nanocrystal. TGA analysis used to measure 1 electrochemical behaviors PMT at were systematically vestigated. As shown re were two strong peaks centered at 1338 1575 cm, which were graphite peaks rmal stability. As shown 2B, a weight crease (250 550 C) obtaed from 1 3A, re a weak anodic peak centered at 1.13 V at bare GC. A strong anodic peak at 1.08, or peaks at 264, 416, 602 cm corresponded to TiC phase (JCPDS: 65 0242)V. crease TiCpeak oxidation titanium dioxide (TiO2) could be seen at CNFs-modified current CNFs creased compared with ( 2A), confirmg weight formation due TiCtonanocrystal. TGA to analysis used to measure air atmosphere (TiC + 2O 2 TiO 2 + 3D CO 2) [19]. amount TiC 40.3%, accordg to that bare GC, attributg to network structure CNFs, which creased active area rmal stability. As shown 2B, a weight crease (250 550 C) obtaed from change weight [21]. Additionally, temperature 5% weight loss 550 C, which regardtoweight, anodic peak PMT observed at a lower. With crease due to TiCpotential oxidation to titanium dioxide (TiO2)potential air V), higher than that CNFs C), demonstratg that much better that rmal (1.02 (TiC peak almost twice compared to40.3% that owned CNFs, suggestg atmosphere +anodic 2O 2 TiO 2 current + CO(390 2) [19]. amount TiC, accordg to stability. electrocatalytic activity hybrid improved with troduction TiC NPs. Meanwhile, change weight [21]. Additionally, temperature 5% weight loss 550 C, which no cathodic peak that appeared (390 reverse dicatg that electrochemical process PMT higher than CNFs C),scan, demonstratg that owned much better rmal 3.2. Electrochemical Behavior irreversible. results suggested that might be employed as a PMT electrochemical probe stability. with high catalytic activity. 3.2. Electrochemical Behavior (A)(A) CVCV curves bare GC, CNFs, -modified electrodes 0.1 M PBS (phm = 4.0) 3. 3. curves bare GC, CNFs, -modified electrodes 0.1 PBS contag 50 µm PMT; (B) Nyquist plots bare GC, CNFs, -modified electrodes. (ph = 4.0) contag 50 μm PMT; (B) Nyquist plots bare GC, CNFs, -modified electrodes. 3. (A) CV curves bare GC, CNFs, (EIS) -modified electrodes 0.1 M PBS electrochemical impedance spectroscopy performed to analyze surface (ph = 4.0) contag μm transfer PMT; (B) Nyquist(Rplots were bare 1.56 GC, CNFs, 103, properties 50 electron resistance 103, 1.23 ct ) values electrochemical behaviors PMT at were systematically vestigated. As shown -modified electrodes. 3A, re a weak anodic peak centered at 1.13 V at bare GC. A strong anodic peak at 1.08 V could be seen at CNFs-modified were peaksystematically current CNFs creased compared electrochemical behaviors PMT at vestigated. As shownwith that bare GC, attributg to 3D network structure CNFs, which creased activeatarea 3A, re a weak anodic peak centered at 1.13 V at bare GC. A strong anodic peak 1.08 With regard to, anodic PMTcreased observed at awith lower V could be seen at CNFs-modified peak peak potential current CNFs compared

Sensors 2019, 19, 1531 5 10 Sensors 2019, 19, x 5.88 10 3 FOR PEER Ω/cm 2 REVIEW 5 10 for CNFs,, bare GC, respectively ( 3B). When CNFs electrochemical modified on process bare GC, PMT value Rct irreversible. decreased, dicatg results that suggested CNFs formed that a fast might electron be employed transfer pathway. as a PMT Inelectrochemical addition, Rct probe with high lower catalytic thanactivity. that CNFs-modified electrode, dicatg electrochemical that TiC NPs could impedance facilitate spectroscopy electron transfer (EIS) between performed film to analyze electrode surface. properties electron transfer resistance (Rct) values were 1.56 10 3, 1.23 10 3, 3.3. Effect ph 5.88 10 3 Ω/cm 2 for CNFs,, bare GC, respectively ( 3B). When CNFs modified on bare effect GC, phvalue vestigated Rct decreased, by dicatg CV. peak that current CNFs formed tensity a fast creased electron from transfer 2.0 pathway. to 4.0 In decreased addition, when Rct ph value furr lower than creased that ( CNFs-modified 4A). Thus, phelectrode, 4.0 dicatg selected asthat an optimal TiC NPs value. could facilitate plot E pa electron verus ph transfer lear, between regression film equation electrode : surface. E pa (mv) = 56/Ph + 1.32 (R = 0.998) ( 4B). obtaed slope value (56 mv/ph) close to ory value (59 mv/ph), suggestg that identical numbers protons electrons participated 3.3. Effect reaction. ph 4. 4. (A) (A) CV CV curves curves -modified -modified electrode electrode 0.1 M PBS 0.1 M PBS present present 10 µm PMT 10 with μm PMT different with ph different values. (B) ph values. effect (B) ph on effect formal potential ph on formal anodic peak potential current. anodic 3.4. Effect peak current. Scan Rate To assess effect ph ketic process, vestigated different by CV. scan rates peak for current PMT oxidation tensity creased were vestigated. from 2.0 to 4.0 peakdecreased potential when shifted toph positive value when furr creased ( scan 4A). rate Thus, (ph 5A), 4.0 suggestg selected that as an optimal electrochemical value. process plot Epa a ketic verus ph limitation, lear, current regression creased equation learly : with Epa (mv) square = 56/Ph root + 1.32 scan (R = rate. 0.998) ( lear regression 4B). obtaed equationslope : value I p (µa) (56 = mv/ph) 5 + 115.6 ν 1/2 close (V/s, to R = 0.999) ory ( value 5B), (59 mv/ph), suggestg suggestg that a diffusion-controlled that identical numbers process had protons taken place electrons at. participated Also, plot reaction. log I p versus log v found to be lear (50 250 mv/s): log I p = 1.42 + 0.62 log ν (R=0.993). slope (0.62) 3.4. Effect higher Scan than Rate oretical value (0.5), suggestg that this reaction a diffusion-controlled process. However, value less than oretical value 1.0 (adsorption-controlled process), illustratg that oxidation PMT at also an adsorption-controlled process [22,23]. above results suggested that oxidation PMT at domated by diffusion process accompanied by adsorption process [24]. For an irreversible reaction, peak potential (E p ) is described as follows [25]: ( ) RT E p = E 0 + ln αnf ( RTk 0 αnf ) + RT ln υ (2) αnf plot E p versus ln ν lear, its equation : E p (V) = 1.18 + 0.06 ln ν (R = 0.992) ( 5C). calculated value αn 0.97. electron number could be obtaed from Tafel curve. As shown 5D, E p proportional to log ν, could be described by followg equation: E p (V) = 1.18 + 0.056 log ν (R = 0.996). Tafel slope b obtaed from followg equation [26,27]: b(log υ) E p = + C (3) 2

Sensors 2019, 19, 1531 6 10 where Slope = b = 2.303RT (1 α)nf Tafel slope b calculated as 0.103. refore, calculated electron transfer number (n) 0.97 (close to 1). Thus, it could be ferred that one proton one electron took part electrochemical Sensors 2019, 19, x FOR reaction. PEER REVIEW 6 10 (4) 5. 5. CVs CVs with with different different scan rates, scan respectively rates, respectively (A); Dependence (A); Dependence peak current peak (I p ) versus current v 1/2 (Ip) (B); versus Dependence v 1/2 (B); Dependence E p versus ln v (C); Ep Dependence versus ln v (C); E p Dependence versus log v (D). Ep versus log v (D). 3.5. Determation PMT by DPV To assess 6A ketic CVsprocess, different with PMTscan rangg rates from for PMT 10 to 30 oxidation µm. were peakvestigated. current creased when peak potential creasgshifted PMT concentration. to positive when This creased result denoted scan that rate effectively ( 5A), electrochemical suggestg that sensg ability electrochemical without process foulg a ketic effect. limitation, As a sensitive electrochemical current creased technique, learly DPV with selected square for PMT root determation. scan rate. As lear expected, regression peak equation current : PMT Ip (μa) creased = 5 + 115.6 learly ν 1/2 (V/s, withr its = concentration 0.999) ( ( 5B), suggestg 6B). lear that a range diffusion-controlled 0.1 600 µm process (R 2 = 0.998). had taken detection place at limit. Also, 33 nm (S/N plot = 3). log Ip lear versus equation log v : found I (µa) to be = 0.72 lear + 0.02 (50 250 C mv/s): log Ip PMT (µm) (R 2 = 0.998) = 1.42 ( + 0.62 log 6C). ν (R=0.993). sensg performances slope (0.62) PMT higher sensor than were compared oretical tovalue or(0.5), methods/materials suggestg that (Table this reaction 1). results a diffusion-controlled displayed that process. exhibited However, a wider lear value range or less lower than detection oretical limit compared value to 1.0 reported (adsorption-controlled results [28 31], suggestg process), illustratg that a promisg oxidation material PMT for PMT at detection. also an adsorption-controlled process [22,23]. above results suggested that oxidation PMT at domated by diffusion process accompanied by adsorption process [24]. For an irreversible reaction, peak potential (Ep) is described as follows [25]: 0 0 RT RTk RT Ep= E + ln + ln (2) αnf αnf αnf υ plot Ep versus ln ν lear, its equation : Ep (V) = 1.18 + 0.06 ln ν (R = 0.992) ( 5C). calculated value αn 0.97. electron number could be obtaed from Tafel curve. As shown 5D, Ep proportional to log ν, could be described by followg equation: Ep (V) = 1.18 + 0.056 log ν (R = 0.996). Tafel slope b obtaed from followg equation [26,27]: where ( log υ ) b Ep = 2 +C (3)

creased learly with its concentration ( 6B). lear range 0.1 600 μm (R 2 = 0.998). detection limit 33 nm (S/N = 3). lear equation : I (μa) = 0.72 + 0.02 CPMT (μm) (R 2 = 0.998) ( 6C). sensg performances PMT sensor were compared to or methods/materials (Table 1). results displayed that exhibited a wider lear range or Sensors lower 2019, detection 19, 1531limit compared to reported results [28 31], suggestg a promisg 7 10 material for PMT detection. 6. CVs (A) DPVs (B) contag different concentrations PMT; PMT; (C) (C) is is calibration calibration plot for plot PMT; for (D) PMT; (D) percentage percentage terferg terferg signals (NOsignals 3, Mg 2+ (NO3, SO 2 4, Mg, Zn 2+ 2+,, SO4 Ca 2+ 2, Na Zn + 2+,, K Ca +, 2+ PO, Na 3 4 +, glucose, K +, PO4 3 vitam, glucose, C, vitam thiabendazole) C, thiabendazole) to PMT. to PMT. Table 1. Sensg performances different methods/materials determation PMT. Table 1. Sensg performances different methods/materials determation PMT. Methods Lear Range (µm) LOD (nm) Ref. Liquid chromatography 0.025 25 9.0 [28] Lear Range MWCNTs-[BMIM][PF6] Methods 0.1 100 LOD 16.0 (nm) [29] Ref. (μm) PANI-β-CD/fMWCNT 10 80 1040 [30] NiCo2O4/RGO/[OMIM]PF6 Liquid chromatography 0.1 140 0.025 25 11.0 9.0 [31] [28] MWCNTs-[BMIM][PF6] 0.1 6000.1 100 33.016.0 This[29] work PANI-β-CD/fMWCNT 10 80 1040 [30] NiCo2O4/RGO/[OMIM]PF6 0.1 140 11.0 [31] 3.6. Reproducibility, Stability, Interference Study 0.1 600 33.0 This work reproducibility as-fabricated sensor also evaluated. relative stard deviation (RSD) for six electrodes 3.4%. RSD each electrode for six measurements 2.35%. To assess stability, a day-to-day stability vestigated. Satisfied stability found, RSD less than 4.7%, demonstratg that sensor possessed good reproducibility stability. acceptable stability can be due to embedded TiC NPs, which could prevent NPs detachment agglomeration from frameworks. anti-terference ability is an important parameter for PMT detection. Some common compounds, such as NO 3, Mg 2+, SO 2 4, Zn 2+, Ca 2+, Na +, K +, PO 3 4, glucose, vitam C, thiabendazole, may coexist with PMT natural samples. Under optimized conditions, oxidization peak current 50 µm PMT dividually measured presence different terferents ir fluence on analytical signal vestigated. results dicated that 50-fold concentration thiabendazole, 100-fold concentrations glucose vitam C, 500-fold concentrations NO 3, Mg 2+, SO 2 4, Zn 2+, Ca 2+, Na +, K +, PO 3 4 showed negligible fluence

Sensors 2019, 19, 1531 8 10 on PMT (current signal change < 5%) ( 6D), dicatg a good anti-terference ability. 3.7. Natural Sample Analyses To evaluate applicability sensor, water, apple, cucumber were selected for quantitative analysis. Satisfactory recoveries (96.50 101.07%) low RSDs (2.5 3.8%) were found (Table 2), dicatg acceptable reliability applicability analytical applications. Table 2. Detection PMT natural samples usg stard addition method. Sample Added (µm) Found (µm) Recovery (%) RSD a (%) Water 0 Nd b 100.00 99.54 99.54 2.8 200.00 202.15 101.07 2.5 Apple 0 Nd b 50.00 48.25 96.50 3.2 100.00 98.06 98.06 2.8 Cucumber 0 Nd b 200.00 202.05 101.03 3.1 300.00 301.21 100.40 3.8 a Relative stard deviation for n = 3; b Mean not detect. 4. Conclusions hybrid fabricated for determation PMT. Homogeneous TiC NPs embedded to CNFs framework observed, which tegrated large surface area unique 3D-networked structure CNF with good electrocatalytic activity TiC NPs. -modified electrode showed an enhanced electrochemical response for oxidation PMT. Wide lear range (0.1 600 µm, R 2 = 0.998) low detection limit (33 nm, S/N = 3) were obtaed. In addition, also showed long-term sensg stability reproducibility. showed potential applications fabrication electrochemical sensors. Author Contributions: Data curation, L.S.; Formal analysis, L.S., T.W. L.L.; Investigation, L.S., T.W. L.L.; Resources, H.W.; Writg Origal Draft Preparation, H.W. Q.W.; Writg review editg, L.S.; H.H.; Project Admistration, Q.G.; Fundg acquisition, Q.G.; All authors discussed results commented on manuscript. Fundg: This work supported by National Natural Science Foundation Cha (21864014 21405065), Natural Science Foundation Jiangxi Provce, Cha (20171BAB213015), Science Technology Project Jiangxi Provce, Cha (20161BCB24005), Project funded by Cha Postdoctoral Science Foundation (2017M611703), foundation Jiangxi Educational Committee (GJJ170169). Conflicts Interest: authors declare that y have no conflict terest. References 1. Ma, J.; Wang, S.; Wang, P.; Ma, L.; Chen, X.; Xu, R. Toxicity assessment 40 herbicides to green alga Raphidocelis subcapitata. Ecotoxicol. Environ. Saf. 2006, 64, 456 462. [CrossRef] [PubMed] 2. Miquel, A.S.; Arben, M.; Salvador, A. Pesticide determation tap water juice samples usg disposable amperometric biosensors made usg thick film technology. Anal. Chim. Acta 2001, 442, 35 44. 3. Baggiani, C.; Baravalle, P.; Giraudi, G.; Tozzi, C. Molecularly imprted solid-phase extraction method for high-performance liquid chromatographic analysis fungicide pyrimethanil we. J. Chromatogr. A 2007, 1141, 158 164. [CrossRef] 4. Cheng, J.; Xia, Y.T.; Zhou, Y.W.; Guo, F.; Chen, G. Application an ultrasound-assisted surfactant-enhanced emulsification microextraction method for analysis diethencarb pyrimethanil fungicides water fruit juice samples. Anal. Chim. Acta 2011, 701, 86 91. [CrossRef] [PubMed]

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