Rapid Detection Method And Instrument For Dairy Safety And Quality Based On Nanofunctional Materials

Dairy products have been known as the ideal diet food for human due to their rich proteins, fat, lactose, minerals, vitamins and amino acids, etc. The per capita consumption of dairy is one of the key indexes of people’s living standards and the dairy industry has become an important part of the development of modern agriculture in the world. The development of dairy industry in China has followed a rapid increasing trend since the year1978. At present, China has become one of the countries with the fastest growth rate in dairy industry in the world. However, the quality of the dairy product is disappointing. The frequent outbreaks of safety incidents in the domestic dairy industry have intensified the dairy safety problems in recent years. In addition to the safety problems, there are also many problems about the quality of dairy products, like the poor quality, counterfeiting, false information about nutrients, and so on. The evaluation of the dairy safety and quality requires the detection methods. The traditional detection methods for the dairy products have some disadvantages including complex operating, limited detection objects, expensive and bulky instrument, and so on.The electrochemical sensing technique has been widely used in the field of biomedicine, environmental monitoring, food and medicine due to the simple equipment, low cost, easy to realize on-site and capable of online testing. The study on electrochemical sensing technique for rapid, sensitive, and accurate detection of toxic and harmful substances in agricultural products is one of the novel and highly attractive research topics in the field of agricultural safety. However, the traditional electrochemical sensors have some drawbacks including low sensitivity, slow response and poor stability. In recent years, the emergence of nanofunctional materials provides a new approach to solve these problems. The research on using nanofunctional materials to improve the performance of the electrochemical sensors has been attracted extensive attention.In this study, a novel and rapid detection method based on the combination of nanotechnology and electrochemical sensing technique for the safety and quality of dairy products was explored. The main detection objects are divided into two types, including toxic and harzerdous substances (hydrogen peroxide and heavy metal ions) and nutritional components (ascorbic acid and calcium ion). Several electrochemical sensors based on nanofunctional materials were constructed to detect the above species with high sensitivity and accuracy. Furthermore, a portable dairy rapid analyser based on nanofunctional material was constructed.Main research contents, results and conclusions are as follows:(1) Electrochemical sensing technique using copper oxide nanoparticle for the rapid detection of hydrogen peroxide residues in dairy productsA novel and rapid method using nanofunctional material for the detection of hydrogen peroxide was established. The copper oxide nanoparticle was synthesized using the chemical aqueous phase precipitation method and was further employed to modify the electrochemical sensor. In this study, in order to improve the stability and anti-interference ability, carbon ionic liquid electrode was employed as the substrate working electrode. Furthermore, we firstly incorporated the copper oxide nanoparticle into the substrate electrode in order to make the developed sensor be renewable. Results showed that there is a linear relationship between the response current obtained from the amperometric i-t curve and the concentration of hydrogen peroxide. Under the optimal detection conditions, the analytical performance of the electrochemical sensor are as follows:the linear response range is1.0×10-6-2.5×10-3mol/L, the linear regression equation is I(μA)=-0.0667+11.3333C (mM) with the linear correlation coefficient of0.9990, the sensitivity is392.99μA mM-1cm-2and the detection limit is0.5×10-6mol/L. Meanwhile, the developed sensor exhibited good selectivity, consistency, reproducibility and stability. Analysis and detection of hydrogen peroxide residues in sterilized milk and yoghurt:using the developed electrochemical analysis method with the enzymatic method for qualitative analysis and the assay time is about2min per milk sample; using standard addition method for quantitative detection and the detection time is about20min per milk sample. Results are consistent with the national standard method (GB23499-2009). The error between these two methods is less than5.0%. These results demonstrate that the novel electrochemical sensing technique using copper oxide nanofunctional material could be used for rapid qualitative analysis and quantitative detection of hydrogen peroxide residues in dairy products.(2) Electrochemical sensing technique using bismuth oxide nanoparticle for the rapid detection of trace heavy metal ions in dairy productsA novel and rapid method using nanofunctional material for the detection of heavy metal ions was established. In this study, we firstly reported an electrochemical sensor based on bismuth oxide nanoparticle. The carbon ionic liquid electrode was used as the substrate electrode and the nanoparticle was doped in the electrode body using the bulk modification method. The electrode can be reused with high repeatability by a simple grinding treatment when the electrode surface is passivated or damaged. In this study, the determination of lead ion and cadmium ion was perfomed using the square-wave anodic stripping voltammetry. The optimal parameters for the detection of lead ion and cadmium ion are obtained as followed:the amount of bismuth oxide nanoparticle in the electrode body is2%, the pH of acetate buffer solution is4.5, deposition time is180s, and deposition potential is-1.2V. Under these optimal conditions, the analytical performance of the electrochemical sensor are as follows:the linear response range for lead ions is1.0～100.0μg/L, the linear regression equation is I(μA)=-0.0211+0.4037C (μg/L) with the linear correlation coefficient of0.9924, the sensitivity is5.92μA (μg/L)-1cm-2and the detection limit is0.21μg/L; the linear response range for cadmium ion is1.0～100.0μg/L, the linear regression equation is I(uA)=-0.0211+0.4037C (μg/L) with the linear correlation coefficient of0.9927, the sensitivity is5.92μA (μg/L)-1cm-2and the detection limit is0.15μg/L. Interference experiments showed that the other metal ions in the solution (concentration200times) exhibit no influence on the detection of lead ion and cadmium ion. Meanwhile, the electrochemical sensor exhibited good consistency, reproducibility and stability. Analysis and detection of lead ion and cadmium ion in whole milk powder and infant formula:using the peak potential of lead ion and cadmium ion obtained by square-wave anodic stripping voltammetry to qualitative analysis and the assay time is about5min per milk sample; quantitative detection using standard addition method and the detection time is about30min per milk sample, the results are consistent with the results obtained by the national strandard methods (GB5009.12-2010and GB/T5009.15-2003). Revovery test showed that the average recoveries are100.8%for lead ion and100.5%for cadmium ion. The above results indicate that the quick qualitative identification and quantitative determination of trace concentration of lead ion and cadmium ion in the dairy could be achieved in the developed electrochemical sensing technique based on bismuth oxide nanofunctional material.(3) Electrochemical sensing technique using single-walled carbon nanotube for the rapid detection of ascorbic acid in dairy productsA novel and rapid method using nanofunctional material for the detection of ascorbic acid was established. In this study, we firstly reported a novel electrochemical sensor consisted of single-walled carbon nanotube and ionic liquid. This sensor showed a high electrocatalytic activity for the oxidation of ascorbic acid which could be used to detect ascorbic acid at the potential of0V. A linear relationship between the oxidation peak current obtained by the differential pulse voltammetry and ascorbic acid concentration could be founded. The analytical performance of the electrochemical sensor are as follows: the linear response range is3.0×10-6～4.2×10-3mol/L, the linear regression equation is I(uA)=0.1603+20.1214C (mM) with the linear correlation coefficient of0.9990, the sensitivity is301.92μA mM-1cm-2and the detection limit is1.0×10-6mol/L. Meanwhile, the developed sensor displayed good selectivity, consistency, reproducibility and stability. Standard addition method was employed for quantitative detection of ascorbic acid in infant formula and fruit milk. Sample test time is about15min per milk sample. The results are consistent with the results obtained by2,6-Dichloroindophenol as recommended by AOAC. These results suggest that the novel electrochemical sensing technique based on carbon nanotube could be used for rapid quantitative detection of ascorbic acid in dairy products. (4) Electrochemical sensing technique using grapheme nanofunctional material for the rapid detection of mineral element calcium ion in dairy productsA novel and rapid method using nanofunctional material for the detection of calcium ion was explored. In this study, we firstly fabricated a solid-contact calcium ion-selective electrode using graphene nanomaterial as the solid-contact layer. Results showed that the graphene-based solid-contact layer in ion-selective electrode could remarkably improve the stability and shorten the response time. The analytical performance of the developed sensor are as follows:the response time (t95%) is less than8s in the whole linear range, the linear response range is10-58～10-1.8mol/L with the linear correlation coefficient of0.9993, the response slope is29.2mV/decade (±0.3mV/decade) and the detection limit is10-6mol/L. The selectivity coefficients are-4.6,-2.2,-2.8,-2.5, and-3.6for Mg2+, K+, Na+, Li+, and NH4+, respectively. Water layer test showed that no water film is formed between the graphene layer and the sensing membrane. The experiments about the interference from oxygen, carbon dioxide, and redox species demonstrated that the developed sensor is no sensitive to these species. The potential drift is about13.7μV/h in the24h continuous monitoring, indicating the excellent potential stability of the developed sensor. The potential error is less than1.2%when using the sensor to successively measure the solutions containing different concentrations of calcium ion. The storage stability of the sensor is three months. Two detection methods including one point calibration procedure and standard addition method were employed to determine calcium ion in sterilized milk and yogurt. Results obtained by these two methods are consistent. Furthermore, compared to the results obtained by the national standard method (GB5413.21-2010), the errors are less than5.0%. Recovery test showed that an average recovery is100.6%for eight additions. The above results demonstrate that the novel solid-contact calcium ion-selective electrode using graphene nanofunctional material as the solid-contact layer could be used to detect calcium ion in dairy products.(5) Construction of portable dairy rapid analyser based on nanofunctional materialsThe feasibility of the construction of portable dairy rapid analyser based on nanofunctional materials was investigated. Four types of disposable electrochemical sensors with low cost, high sensitivity and good consistency were developed using screen-printing technique, including hydrogen peroxide sensor using electrochemically reduced graphene nanomaterial, heavy metal ions sensor using bismuth oxide nanoparticle, ascorbic acid sensor using chemically reduced graphene nanomaterial, and calcium ion sensor using electrochemically reduced graphene nanomaterial and calcium ion-selective membrane. Ten types of electrochemical analytical techniques and three types of electrode system could be achieved on the developed miniaturizied analyser. The protable dairy rapid analyser was constructed by the disposable sensors and the miniaturizied analyser. This analyzer can achieve multi-channel simulataneous detection of various analytes or analysis of several samples. Futhermore, it is protable and possesses high accuracy, high precision, fast speed and continuous detection. Results show that the developed portable analyser could be used for the rapid detection of the toxic-harzerdous substances and nutritional components in dairy.