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Abstract A test strip was developed to rapidly detect fluoroquinolones in foods by colloidal gold immunochromatography method in combination with a food safety analyzer. The results showed that the test strip has the detection sensitivity of 20 g/L for enrofloxacin， sarafloxacin， difloxacin， ofloxacin， norfloxacin， ciprofloxacin， pefloxacin， flumequine and danofloxacin， and the detection sensitivity of 40 g/L for enoxacin and oxolinic acid. The test strip consumes only 10 min for detection， and the false positive rate and the false negative rate are both zero. The test strip can accurately， reliably and easily detect residual fluoroquinolones in foods， and is suitable for onsite detection of a large number of samples.
Key words Fluoroquinolones; Colloidal gold strip; Food safety analyzer; Rapid detection
Fluoroquinolones （FQs） are important broadspectrum antibiotics， including ciprofloxacin （CIP）， enrofloxacin （ENR）， sarafloxaxcin （SAR）， and danoxacin （DAN） and difloxacin （DIF）. These drugs are widely used in animal husbandry to prevent and treat animal diseases， but there has been a problem of animalderived veterinary drug residues. Fluoroquinolone residues in animalderived foods， in addition to toxic side effects to consumers， can easily induce resistance to human pathogens[1]. In addition， China is an exporter of animalderived foods， and over the years， the international market pressure on the export of agricultural and livestock products has increased due to the problem of drug residues.
At present， the qualitative detection techniques for the determination of fluoroquinolone residues in animal tissues include microbiological method， fluorescence spectrophotometry， enzymelinked immunoassay， etc.; and the quantitative detection techniques include high performance liquid chromatography （HPLC）， liquid chromatographymass spectrometry （LCMS）， and capillary zone electrophoresis and micellar electrokinetic capillary chromatography. The Ministry of Agriculture issued the residue detection method for enrofloxacin， ciprofloxacin， oxolinic acid and flumequine in animal foods in Announcement No. 236， 45. The standard detection methods for other FQs have not been specified.
In existing rapid detection methods， the author found that the colloidal gold immunochromatography test strip method has the characteristics of high sensitivity， short detection time， convenient carrying and simple and onsite operation[2]. Therefore， the study explored and developed a rapid colloidal gold test strip for fluoroquinolone drugs， which is used in combination with a food safety analyzer. In the food safety field， the stored test strip detection data can be uploaded to a notebook computer with a wireless network card through a data line; the notebook computer uploads the data to a main server through a wireless network; and the monitoring room of government departments and the main monitoring room of enterprises can view the database in the server through software. The detection data in the subserver can be viewed by opening the icon of the subserver from the main server interface in the software; the information in the subserver interface includes： detection date， detection time， sample number， experimenter， detection item， detection value， and red and green indicator lights; and if the red indicator light appears， the drug in the sample exceeds the standard， and the system will give an alarm to the head of the government department. Information exchange and communication is performed applying the IoT technology to realize intelligent identification， positioning， tracking， monitoring and management， to thereby realize realtime monitoring of food safety， and the establishment of a traceable database achieves seamless sensing， safe control and reliable tracing from farmland to diningtable， thereby protecting human health and maintaining normal import and export trade. The software interface is shown in Fig. 1. Materials and Methods
Materials and instruments
Chloroauric acid， Sigma， USA; trisodium citrate and potassium carbonate， Guangzhou Chemical Reagent Factory; enrofloxacin， salsalfloxacin， difloxacin， ofloxacin， norfloxacin， ciprofloxacin， enoxacin， pefloxacin， flumequine， oxolinic acid and danofloxacin standards， China Institute of Veterinary Drug Control; nitrocellulose membrane （NC membrane）， glass fiber， sample pad and absorbent paper， WuXi Biologics; XYZ 3000 platform system and test strip cutter， Biodot Company， USA; freezedrying machine， Beijing Songyuan Huaxing Biotechnology Co.， Ltd.; UVVis spectrophotometer， Eppendorf Company; refrigerated centrifuge， Hunan Xiangli Scientific Instrument Co.， Ltd.; magneticstirring heater， Henan Shengya Instrument Co.， Ltd.; food safety analyzer GT710， Beijing Kwinbon Biotechnology Co.， Ltd.
Methods
Preparation of fluoroquinolonecarrier protein conjugate
Fluoroquinolones are small molecules that are only reactive， have no immunogenicity and do not induce an immune response in the body. They must be coupled to a macromolecular carrier protein to be immunogenic.
At first， 1 mmol of norfloxacin was dissolved in 15 ml of chloroform， followed by the addition of 2 mmol of N，N′dicyclohexylcarbodiimide （DCC）， a proper amount of 4dimethylaminopyridine （DMAP） catalyst and 1.5 mmol of tertbutyl 3aminopropanoate. The mixture was stirred at room temperature for 5 h， and thin layer chromatography （TLC） was performed to observe the disappearance of the material. The solution was filtered， and the liquid phased was washed with water and dried with anhydrous Na2S2O4. The liquid phase was purified by column chromatography （eluent： ethyl acetate/petroleum ether， 1/5）. The above product was dissolved in glacial acetic acid and stirred at room temperature for 2 h， and thin layer chromatography （TLC） was performed to observe the disappearance of the material. The solvent was evaporated under reduced pressure， and the obtained viscous material was dissolved in 1 mol/L NaOH solution， and the pH was adjusted to 3-5. The material was then extracted with ethyl acetate， and dried. Chromatography purification （eluent： ethyl acetate/petroleum ether， 1/1） was performed， giving the fluoroquinolone hapten. The process is shown in Fig. 2. The product can then be attached to the protein by a mixed anhydride method.
Preparation of monoclonal antibody against fluoroquinolones
The immunogen （FQSBSA） prepared above was used to carry out animal immunization， obtaining a hybridoma cell line D31 that stably secretes monoclonal antibody against fluoroquinolones. The hybridoma cell line was preserved in China General Microbiological Culture Collection Center （CGMCC） on March 12， 2012， under the collection registration number CGMCC NO.5885. Preparation of colloidal goldlabeled monoclonal antibody against fluoroquinolones
Preparation of colloidal gold
At first， 1% chloroauric acid was diluted to 0.01% （by weight） with double distilled deionized water， stirred and boiled on a magneticstirring heater. Then， 2.5 ml of 1% trisodium citrate was added per 100 ml of 0.01% chloroauric acid， and stirring and heating were continued until the liquid was red. The system was cooled to room temperature， and water was added to make up the water loss. The prepared colloidal gold looked pure， clear， free of deposits and floats， as shown in Fig. 3.
Preparation of colloidal goldlabeled monoclonal antibody against fluoroquinolones
Under magnetic stirring， the pH of the colloidal gold was adjusted to 7.0 with 0.2 mol/L potassium carbonate， and the abovementioned monoclonal antibody for fluoroquinolone drugs was added to the colloidal gold solution according to the standard of 50-100 g/ml， and stirring and mixing were continued for 30 min. 10% BSA was added to the final BSA concentration of 1% （by volume） in the colloidal gold solution， followed by 30 min of standing. The solution was centrifuged at 12 000 rpm and 4 for 30 min. The supernatant was discarded， and the precipitate was washed twice with reconstitution buffer， and was resuspended in the reconstitution buffer having a volume 1/20 of the original colloidal gold volume， obtaining the monoclonal antibody solution containing 50 g/ml colloidal goldlabeled monoclonal antibody for fluoroquinolone drugs， which was stored at 4 for later use.
Assembly of the test strip
The sample absorption pad， reaction membrane， absorbent pad and protection membrane were assembled. The distal end of the sample absorption pad was connected to the proximal end of the reaction membrane; the distal end of the reaction membrane was connected to the proximal end of the absorbent pad; and the proximal end of the sample absorption pad was aligned with the proximal end of the bottom plate， and the distal end of the absorption pad was aligned with the distal end of the bottom plate. The two ends of the test strip were adhered to the protection film.
Detection test of the test strip
Sensitivity test
The enrofloxacin， salsalfloxacin， difloxacin， ofloxacin， norfloxacin， ciprofloxacin， enoxacin， pefloxacin， flumequine， oxolinic acid and danofloxacin standards were diluted to the following concentrations： 0， 10， 20， 40 g/L （enrofloxacin， salsalfloxacin， difloxacin， ofloxacin， norfloxacin， ciprofloxacin， pefloxacin， flumequine and danofloxacin）， 0， 20， 40， 80 g/L （enoxacin and oxolinic acid）. The dilution used 0.2 mol/L of phosphate buffer （pH 7.2）. Testing was performed with the test strip， with 3 replicates. Specificity test
Specificity is generally represented by cross reaction rate， which refers to the ability of an antibody to bind to an antigenic determinant having a different structure. Other drugs commonly detected in food： melamine， sulfonamides， chloramphenicol， macrolides， aminoglycosides and tetracyclines， were diluted with 0.2 mol/L PBS （pH 7.2） to the final concentration of 500 g/L. Then， testing was performed with the test strip， with 3 replicates.
Detection of the negative and positive rates of the test strip
At first， 20 positive pork samples with a known enrofloxacin content greater than 20 g/L and 20 negative pork samples with a concentration less than 20 g/L were taken and tested with the fluoroquinolone test strip， to calculate the negative and positive rates.
Use of food safety analyzer
Although the color depth of the T line and C line of the test strip can be used to quickly interpret the result， the test result of the test strip has problems such as high subjectivity， unsuccessful storage， and inability to perform data analysis. There is a risk of misrecording and missing recording of the test data of the test strip， and the accuracy of the data cannot be guaranteed. Therefore， error in human interpretation can be effectively avoided together with the food safety analyzer readings， and realtime online monitoring can be realized in combination with the IoT technology.
This study used a food safety analyzer. The food safety analyzer has a 7inch colored capacitive touch screen and supports builtin 3G/4G. Its reading speed is less than 2 s， with reading accuracy： CV <1%. It has builtin battery and can be connected to the printer. It can store more than 1 million data， and can realize remote data transmission and monitoring in combination with the Internet of Things and database system. When in use， the colordeveloped test strip is inserted into the food safety analyzer， and after color development and stacking line by line， the value is measured， giving the measured value which is used to derive the concentration value.
Results and Analysis
Sensitivity and specificity results of the test strip
Sensitivity test
When dropping 0 and 10 g/L of enrofloxacin， sarafloxacin， difloxacin， ofloxacin， norfloxacin， ciprofloxacin， pefloxacin， flumequine and danofloxacin and 0 and 20 g/L of enoxacin and oxolinic acid， the test strip showed two red lines visible to naked eyes， and the detection results obtained with the food safety analyzer were negative. When dropping 20 and 40 g/L enrofloxacin， sarafloxacin， difloxacin， ofloxacin， norfloxacin， ciprofloxacin， pefloxacin， flumequine and danofloxacin and 40 and 80 g/L enoxacin and oxolinic acid， the quality control area of the test strip developed color， but the detection area did not develop color， and positive results were obtained by the food safety analyzer. The results are shown in Table 1. Discussion
At present， most studies on fluoroquinolones in foods at home and abroad use HPLC with fluorescence detector[3-5]. Although the instrument method is sensitive， accurate， specific， and has good resolution， but there are many disadvantages such as relatively complicated pretreatment of samples， long detection cycle， tedious program， need for numerous reagents and requirement for special technicians in operation， and the instruments are expensive， energywasting. It is difficult to meet the requirements of food enterprises of various scales. The development trend of the rapid detection industry of food safety is that under the premise of ensuring the detection accuracy， the detection time is as short as possible; if detection sensitivity is higher， the sensitivity of the rapid detection method will be required to be close to or reach the level of the analytical instrument and satisfy the requirements of ultratrace index detection; and the detection instrument is developing toward miniaturization and automation. The integration of detection methods requires a technique for simultaneously measuring multiple components by one test.
The sensitivity of this test strip to enrofloxacin， sarafloxacin， difloxacin， ofloxacin， norfloxacin， ciprofloxacin， pefloxacin， flumequine and danofloxacin is 20 g/ L， and the detection sensitivity to enoxacin and oxolinic acid is 40 g/L. At the same time， the test strip has good specificity， and the false positive rate and the false negative rate are both zero.
Colloidal gold test strip has high detection speed （10 min）， low detection cost and simple operation. The food safety analyzer is small in size and light in weight， and can store and trace the data quickly under of field conditions. Through the selfdeveloped test strip and food safety analyzer， combined with the Internet of Things technology， the rapid and onsite detection of pollutants in agricultural products can be effectively connected with the realtime monitoring by government or enterprises. The detection method is especially suitable for being widely used in market monitoring and testing， temporary sampling and inspection and inspection work of the grassroots testing laboratories and government departments in China， and can realize convenient and rapid biotechnological detection in the field of safe circulation and consumption of foods， thereby solving the problem that it is difficult for some grassroots units to carry out the detection and monitoring of residues in foods due to the lack of equipment and funding and providing testing techniques and products for food safety inspection by agricultural quality inspection department， health department， business administration， aquaculture and other institutions， which is conducive to the implementation of food safety monitoring programs[6]. As the food safety inspection methods are required to be improved continuously， researchers in this field are working harder to jointly promote the development of Chinas food safety detection techniques. References
[1]PAN MF， WANG JP， WANG S， et al. Development of fluoroquinolones residue detection with chromatography in food[J]. Food & Machinery， 2009， 25（5）： 129-132. （in Chinese）
[2]LAI WH， XIONG YH， CHEN GM， et al. Preparation of colloidal gold strip for rapid detection of ochratoxin A[J]. Food Science， 2005， 26（5）： 204-207. （in Chinese）
[3]DONG ZY， ZHAO XF， GONG XJ， et al. Study on detection method of fluroquinolones residues in milk[J]. Chinese Journal of Veterinary Drug， 2008， 42（10）： 14-16. （in Chinese）
[4]N VAN HOOF， K DE WASCH， L OKERMAN， et al. Validation of a liquid chromatographytandem mass spectrometric method for the quantification of eight quinolones in bovine muscle， milk and aquacultured products[J]. Analytica Chimica Acta， 2005 （529）： 265-272.
[5]RAO Y， ZENG ZL， YANG GX， et al. Confirmation of fluoroquinolone residues in milk by liquid chromatographytandem mass spectrometry[J]. Scientia Agricultura Sinica， 2007， 40（5）： 1033-1041. （in Chinese）
[6]DENG XL， LAI WH， XU Y. Study on gold immunochromatography assay for rapid detection of aflatoxin B1[J]. Food Science， 2007， 28（2）： 232-236. （in Chinese）
Key words Fluoroquinolones; Colloidal gold strip; Food safety analyzer; Rapid detection
Fluoroquinolones （FQs） are important broadspectrum antibiotics， including ciprofloxacin （CIP）， enrofloxacin （ENR）， sarafloxaxcin （SAR）， and danoxacin （DAN） and difloxacin （DIF）. These drugs are widely used in animal husbandry to prevent and treat animal diseases， but there has been a problem of animalderived veterinary drug residues. Fluoroquinolone residues in animalderived foods， in addition to toxic side effects to consumers， can easily induce resistance to human pathogens[1]. In addition， China is an exporter of animalderived foods， and over the years， the international market pressure on the export of agricultural and livestock products has increased due to the problem of drug residues.
At present， the qualitative detection techniques for the determination of fluoroquinolone residues in animal tissues include microbiological method， fluorescence spectrophotometry， enzymelinked immunoassay， etc.; and the quantitative detection techniques include high performance liquid chromatography （HPLC）， liquid chromatographymass spectrometry （LCMS）， and capillary zone electrophoresis and micellar electrokinetic capillary chromatography. The Ministry of Agriculture issued the residue detection method for enrofloxacin， ciprofloxacin， oxolinic acid and flumequine in animal foods in Announcement No. 236， 45. The standard detection methods for other FQs have not been specified.
In existing rapid detection methods， the author found that the colloidal gold immunochromatography test strip method has the characteristics of high sensitivity， short detection time， convenient carrying and simple and onsite operation[2]. Therefore， the study explored and developed a rapid colloidal gold test strip for fluoroquinolone drugs， which is used in combination with a food safety analyzer. In the food safety field， the stored test strip detection data can be uploaded to a notebook computer with a wireless network card through a data line; the notebook computer uploads the data to a main server through a wireless network; and the monitoring room of government departments and the main monitoring room of enterprises can view the database in the server through software. The detection data in the subserver can be viewed by opening the icon of the subserver from the main server interface in the software; the information in the subserver interface includes： detection date， detection time， sample number， experimenter， detection item， detection value， and red and green indicator lights; and if the red indicator light appears， the drug in the sample exceeds the standard， and the system will give an alarm to the head of the government department. Information exchange and communication is performed applying the IoT technology to realize intelligent identification， positioning， tracking， monitoring and management， to thereby realize realtime monitoring of food safety， and the establishment of a traceable database achieves seamless sensing， safe control and reliable tracing from farmland to diningtable， thereby protecting human health and maintaining normal import and export trade. The software interface is shown in Fig. 1. Materials and Methods
Materials and instruments
Chloroauric acid， Sigma， USA; trisodium citrate and potassium carbonate， Guangzhou Chemical Reagent Factory; enrofloxacin， salsalfloxacin， difloxacin， ofloxacin， norfloxacin， ciprofloxacin， enoxacin， pefloxacin， flumequine， oxolinic acid and danofloxacin standards， China Institute of Veterinary Drug Control; nitrocellulose membrane （NC membrane）， glass fiber， sample pad and absorbent paper， WuXi Biologics; XYZ 3000 platform system and test strip cutter， Biodot Company， USA; freezedrying machine， Beijing Songyuan Huaxing Biotechnology Co.， Ltd.; UVVis spectrophotometer， Eppendorf Company; refrigerated centrifuge， Hunan Xiangli Scientific Instrument Co.， Ltd.; magneticstirring heater， Henan Shengya Instrument Co.， Ltd.; food safety analyzer GT710， Beijing Kwinbon Biotechnology Co.， Ltd.
Methods
Preparation of fluoroquinolonecarrier protein conjugate
Fluoroquinolones are small molecules that are only reactive， have no immunogenicity and do not induce an immune response in the body. They must be coupled to a macromolecular carrier protein to be immunogenic.
At first， 1 mmol of norfloxacin was dissolved in 15 ml of chloroform， followed by the addition of 2 mmol of N，N′dicyclohexylcarbodiimide （DCC）， a proper amount of 4dimethylaminopyridine （DMAP） catalyst and 1.5 mmol of tertbutyl 3aminopropanoate. The mixture was stirred at room temperature for 5 h， and thin layer chromatography （TLC） was performed to observe the disappearance of the material. The solution was filtered， and the liquid phased was washed with water and dried with anhydrous Na2S2O4. The liquid phase was purified by column chromatography （eluent： ethyl acetate/petroleum ether， 1/5）. The above product was dissolved in glacial acetic acid and stirred at room temperature for 2 h， and thin layer chromatography （TLC） was performed to observe the disappearance of the material. The solvent was evaporated under reduced pressure， and the obtained viscous material was dissolved in 1 mol/L NaOH solution， and the pH was adjusted to 3-5. The material was then extracted with ethyl acetate， and dried. Chromatography purification （eluent： ethyl acetate/petroleum ether， 1/1） was performed， giving the fluoroquinolone hapten. The process is shown in Fig. 2. The product can then be attached to the protein by a mixed anhydride method.
Preparation of monoclonal antibody against fluoroquinolones
The immunogen （FQSBSA） prepared above was used to carry out animal immunization， obtaining a hybridoma cell line D31 that stably secretes monoclonal antibody against fluoroquinolones. The hybridoma cell line was preserved in China General Microbiological Culture Collection Center （CGMCC） on March 12， 2012， under the collection registration number CGMCC NO.5885. Preparation of colloidal goldlabeled monoclonal antibody against fluoroquinolones
Preparation of colloidal gold
At first， 1% chloroauric acid was diluted to 0.01% （by weight） with double distilled deionized water， stirred and boiled on a magneticstirring heater. Then， 2.5 ml of 1% trisodium citrate was added per 100 ml of 0.01% chloroauric acid， and stirring and heating were continued until the liquid was red. The system was cooled to room temperature， and water was added to make up the water loss. The prepared colloidal gold looked pure， clear， free of deposits and floats， as shown in Fig. 3.
Preparation of colloidal goldlabeled monoclonal antibody against fluoroquinolones
Under magnetic stirring， the pH of the colloidal gold was adjusted to 7.0 with 0.2 mol/L potassium carbonate， and the abovementioned monoclonal antibody for fluoroquinolone drugs was added to the colloidal gold solution according to the standard of 50-100 g/ml， and stirring and mixing were continued for 30 min. 10% BSA was added to the final BSA concentration of 1% （by volume） in the colloidal gold solution， followed by 30 min of standing. The solution was centrifuged at 12 000 rpm and 4 for 30 min. The supernatant was discarded， and the precipitate was washed twice with reconstitution buffer， and was resuspended in the reconstitution buffer having a volume 1/20 of the original colloidal gold volume， obtaining the monoclonal antibody solution containing 50 g/ml colloidal goldlabeled monoclonal antibody for fluoroquinolone drugs， which was stored at 4 for later use.
Assembly of the test strip
The sample absorption pad， reaction membrane， absorbent pad and protection membrane were assembled. The distal end of the sample absorption pad was connected to the proximal end of the reaction membrane; the distal end of the reaction membrane was connected to the proximal end of the absorbent pad; and the proximal end of the sample absorption pad was aligned with the proximal end of the bottom plate， and the distal end of the absorption pad was aligned with the distal end of the bottom plate. The two ends of the test strip were adhered to the protection film.
Detection test of the test strip
Sensitivity test
The enrofloxacin， salsalfloxacin， difloxacin， ofloxacin， norfloxacin， ciprofloxacin， enoxacin， pefloxacin， flumequine， oxolinic acid and danofloxacin standards were diluted to the following concentrations： 0， 10， 20， 40 g/L （enrofloxacin， salsalfloxacin， difloxacin， ofloxacin， norfloxacin， ciprofloxacin， pefloxacin， flumequine and danofloxacin）， 0， 20， 40， 80 g/L （enoxacin and oxolinic acid）. The dilution used 0.2 mol/L of phosphate buffer （pH 7.2）. Testing was performed with the test strip， with 3 replicates. Specificity test
Specificity is generally represented by cross reaction rate， which refers to the ability of an antibody to bind to an antigenic determinant having a different structure. Other drugs commonly detected in food： melamine， sulfonamides， chloramphenicol， macrolides， aminoglycosides and tetracyclines， were diluted with 0.2 mol/L PBS （pH 7.2） to the final concentration of 500 g/L. Then， testing was performed with the test strip， with 3 replicates.
Detection of the negative and positive rates of the test strip
At first， 20 positive pork samples with a known enrofloxacin content greater than 20 g/L and 20 negative pork samples with a concentration less than 20 g/L were taken and tested with the fluoroquinolone test strip， to calculate the negative and positive rates.
Use of food safety analyzer
Although the color depth of the T line and C line of the test strip can be used to quickly interpret the result， the test result of the test strip has problems such as high subjectivity， unsuccessful storage， and inability to perform data analysis. There is a risk of misrecording and missing recording of the test data of the test strip， and the accuracy of the data cannot be guaranteed. Therefore， error in human interpretation can be effectively avoided together with the food safety analyzer readings， and realtime online monitoring can be realized in combination with the IoT technology.
This study used a food safety analyzer. The food safety analyzer has a 7inch colored capacitive touch screen and supports builtin 3G/4G. Its reading speed is less than 2 s， with reading accuracy： CV <1%. It has builtin battery and can be connected to the printer. It can store more than 1 million data， and can realize remote data transmission and monitoring in combination with the Internet of Things and database system. When in use， the colordeveloped test strip is inserted into the food safety analyzer， and after color development and stacking line by line， the value is measured， giving the measured value which is used to derive the concentration value.
Results and Analysis
Sensitivity and specificity results of the test strip
Sensitivity test
When dropping 0 and 10 g/L of enrofloxacin， sarafloxacin， difloxacin， ofloxacin， norfloxacin， ciprofloxacin， pefloxacin， flumequine and danofloxacin and 0 and 20 g/L of enoxacin and oxolinic acid， the test strip showed two red lines visible to naked eyes， and the detection results obtained with the food safety analyzer were negative. When dropping 20 and 40 g/L enrofloxacin， sarafloxacin， difloxacin， ofloxacin， norfloxacin， ciprofloxacin， pefloxacin， flumequine and danofloxacin and 40 and 80 g/L enoxacin and oxolinic acid， the quality control area of the test strip developed color， but the detection area did not develop color， and positive results were obtained by the food safety analyzer. The results are shown in Table 1. Discussion
At present， most studies on fluoroquinolones in foods at home and abroad use HPLC with fluorescence detector[3-5]. Although the instrument method is sensitive， accurate， specific， and has good resolution， but there are many disadvantages such as relatively complicated pretreatment of samples， long detection cycle， tedious program， need for numerous reagents and requirement for special technicians in operation， and the instruments are expensive， energywasting. It is difficult to meet the requirements of food enterprises of various scales. The development trend of the rapid detection industry of food safety is that under the premise of ensuring the detection accuracy， the detection time is as short as possible; if detection sensitivity is higher， the sensitivity of the rapid detection method will be required to be close to or reach the level of the analytical instrument and satisfy the requirements of ultratrace index detection; and the detection instrument is developing toward miniaturization and automation. The integration of detection methods requires a technique for simultaneously measuring multiple components by one test.
The sensitivity of this test strip to enrofloxacin， sarafloxacin， difloxacin， ofloxacin， norfloxacin， ciprofloxacin， pefloxacin， flumequine and danofloxacin is 20 g/ L， and the detection sensitivity to enoxacin and oxolinic acid is 40 g/L. At the same time， the test strip has good specificity， and the false positive rate and the false negative rate are both zero.
Colloidal gold test strip has high detection speed （10 min）， low detection cost and simple operation. The food safety analyzer is small in size and light in weight， and can store and trace the data quickly under of field conditions. Through the selfdeveloped test strip and food safety analyzer， combined with the Internet of Things technology， the rapid and onsite detection of pollutants in agricultural products can be effectively connected with the realtime monitoring by government or enterprises. The detection method is especially suitable for being widely used in market monitoring and testing， temporary sampling and inspection and inspection work of the grassroots testing laboratories and government departments in China， and can realize convenient and rapid biotechnological detection in the field of safe circulation and consumption of foods， thereby solving the problem that it is difficult for some grassroots units to carry out the detection and monitoring of residues in foods due to the lack of equipment and funding and providing testing techniques and products for food safety inspection by agricultural quality inspection department， health department， business administration， aquaculture and other institutions， which is conducive to the implementation of food safety monitoring programs[6]. As the food safety inspection methods are required to be improved continuously， researchers in this field are working harder to jointly promote the development of Chinas food safety detection techniques. References
[1]PAN MF， WANG JP， WANG S， et al. Development of fluoroquinolones residue detection with chromatography in food[J]. Food & Machinery， 2009， 25（5）： 129-132. （in Chinese）
[2]LAI WH， XIONG YH， CHEN GM， et al. Preparation of colloidal gold strip for rapid detection of ochratoxin A[J]. Food Science， 2005， 26（5）： 204-207. （in Chinese）
[3]DONG ZY， ZHAO XF， GONG XJ， et al. Study on detection method of fluroquinolones residues in milk[J]. Chinese Journal of Veterinary Drug， 2008， 42（10）： 14-16. （in Chinese）
[4]N VAN HOOF， K DE WASCH， L OKERMAN， et al. Validation of a liquid chromatographytandem mass spectrometric method for the quantification of eight quinolones in bovine muscle， milk and aquacultured products[J]. Analytica Chimica Acta， 2005 （529）： 265-272.
[5]RAO Y， ZENG ZL， YANG GX， et al. Confirmation of fluoroquinolone residues in milk by liquid chromatographytandem mass spectrometry[J]. Scientia Agricultura Sinica， 2007， 40（5）： 1033-1041. （in Chinese）
[6]DENG XL， LAI WH， XU Y. Study on gold immunochromatography assay for rapid detection of aflatoxin B1[J]. Food Science， 2007， 28（2）： 232-236. （in Chinese）