## 3 Results & Discussion
### Electrochemical and PANI@CNT/CNC SPME MN-Coupled GC-MS Analysis of Kiwi, Tea, and Coffee Samples  
The ability of PANI@CNT/CNC SPME MN to analyze fruit and beverage samples in situ using both electrochemistry and GC-MS was then examined. First, the PANI@CNT/CNC SPME MN was used to poke into a kiwi fruit, along with a reference and counter electrode as shown in Figure 8a, and were used to semi-quantitatively determine the combined antioxidant content at different penetration depths and ripening times of the kiwi using CV. Different CV responses between 0-day and 3-day kiwi fruit were observed as shown in Figure 8b, potentially due to the changes in antioxidant capacity due to fluctuation of compounds such as ascorbic acid that typically occurs as the fruit ripens [35; 36]. Following CV analysis, the PANI@CNT/CNC SPME MN was coupled with GC-MS to identify various compounds found within kiwi fruit. Labeled total ion chromatograms (TICs) for GC-MS analysis of kiwi surface and core are shown in Figure 9a,b, respectively. Associated lists of potential compounds identified through NIST library database in each kiwi sample depth analysis are shown in Figure 9c,d. Volatile esters, such as the methyl and ethyl esters of butanoic acid [37], and various sugar esters were easily identified (Figure 9). This verifies the ability of the PANI@CNT/CNC SPME MN to be dually usable as an electrochemical sensor and for SPME GC/MS analysis. The fact that the PANI@CNT/CNC are entrained within the stainless steel needle safeguards the SPME electrode from destruction during sample penetration, extraction, and GC/MS injection, hence their evidenced robustness. Next, the PANI@CNT/CNC SPME MN was used to electrochemically determine the 3-CQA content in dark roast coffee. Figure 10a show the overlaid CVs obtained from the analysis of 0.10 M phosphate buffer blank, coffee (in 0.1 M phosphate buffer), and 330 mg/L 3-CQA (in 0.10 M phosphate buffer) analyzed using the PANI@CNT/CNC SPME MN. 3-CQA is one of the many antioxidant compounds contained within coffee, and its total content depends on the conditions of coffee preparation [32; 33]. Figure 10b show associated standard addition plot of \(\triangle\)Current as a function of 3-CQA concentration spiked in the beverage sample. The excellent linear regression (R\({}^{2}\) of 0.99) of the calibration plot is evidence to the performance of PANI@CNT/CNC SPME MN in the analysis of 3-CQA in coffee, a real-world sample with complex matrices. The average% RSD across the different standard spikes in the coffee samples were 1.7%, indicative of excellent precision of the MN electrode. By using the standard addition calibration plot, the amount of 3-CQA was determined to be 2.2 \(\pm\) 0.2 mg/mL, which aligns well with the total chlorogenic acid content found in regular dark roast coffee [33]. To confirm the reproducibility of the PANI@CNT/CNC MN sensors under electrochemical conditions, we further tested  
Figure 7: (**a**) Overlaid CVs obtained from the analysis of 0.10 M phosphate buffer blank, 75, and 450 mg/L 3-caffeoylquinic acid (3-CQA) (in 0.10 M phosphate buffer) taken using the PANI@CNT/CNC SPME MN. (**b**) Associated 3-CQA concentration vs. \(\triangle\)Current linear plot determined by averaging the 3-CQA oxidation peak current signal in the \(-\)0.5 V-0.0 V.  
triplicate sensors for over one month period, analyzing a 300 mg/L 3-CQA for \(\sim\)15 times, and the% RSD was determined to be \(\sim\)1.7% for each day analysis and \(\sim\)3.0% RSD, when data was averaged across all the runs for all the three sensor electrodes. Using the PANI@CNT/CNC SPME MN sensor and the CV results demonstrated herewith, selectivity of electroactive analytes would be based on the peak currents at different voltages. While this does not yield perfect selectivity as certain electroactive analytes may have overlapping redox peaks, it should be noted that highly selective sensors can be obtained using the PANI@CNT/CNC MN platform by integrating additional layers of biological and biomimetic molecular receptors.