# Exploring the Potential of Sensing for Breast Cancer Detection
## 6 Challenges for Existing Techniques and Prospects
\begin{table}
\begin{tabular}{c c c c c} \hline
**Type of Biosensor** & **Target** & **Linear Range** & **Limit of Detection** & **References** \\ \hline SPR & HER2 & \(10^{-12}\)-\(10^{-6}\) g/mL & \(9.3\times 10^{-9}\)/mL & [183] \\  & MCF-7 & \(10^{4}\)-\(10^{6}\)cells/mL & 500 cells/mL & [184] \\ Calorimetric & BRCA1 & 1 fM-100 pM & 0.34 fM & [99] \\  & BRCA1 & \(10^{-12}\) M–\(10^{-18}\) M & \(10^{-18}\) M & [98] \\ SERS & CA153 & - & 0.0001 U/mL & [185] \\ ECL & HER2 & 0–900 pg/mL & 20.4 pg/mL & [186] \\  & MCF-7 & 10–100 cells & 10 cells & [187] \\  & CA19-9 & 0.0001–10 U/mL & 0.000046 U/mL & [188] \\  & miRNA-21 & 100 nM–100 pM & 19.05 nM & [189] \\  & CA19-9 & 0.0005–150 U/mL & 0.0002 U/mL & [190] \\  & MUC1 & 1 fg/mL–1 ng/mL & 0.62 fg/mL & [191] \\  & HER2 & 1 fM–1.0 nM & 1 fM & [192] \\ QCM & MCF-7 & \(10^{2}\)–\(10^{5}\)cells/mL & 430 cells/mL & [193] \\  & MCF-7 & \(10^{2}\)–\(10^{7}\)cells/mL & 32 cells/mL & [194] \\  & MDA MB 231 & 12 cells/mL & [195] \\ Fluorescence & CA125 & \(10^{-2}\)–\(127\) U/mL & \(10^{-4}\) U/mL & [196] \\  & CYP1A1 & - & 1 pg/mL & [197] \\  & miRNA-21 & 1 pM–10 nM & 55 fM & [198] \\  & miRNA-21 & - & 18.7 pM & [199] \\ Microfluidic & HER2 & 1 fM–100 nM & 1 pM & [200] \\  & CA15-3 & 10–1000 \(\mu\)U/mL & 6.0 \(\mu\)U/mL & [201] \\  & CEA & - & 0.2 ng/mL & [202] \\  & Glypician-1 & - & 10 exosome/\(\mu\)L & [203] \\  & PTK7 & - & 0.4 nM & [204] \\ MIP & CA 15-3 & 0.1–100 U/mL & 0.10 U/mL & [134] \\  & HER2 & 1–200 ng/mL & 0.43 ng/mL & [205] \\  & CA 15-3 & 5–50 U/mL & 1.5 U/mL & [206] \\ Field effect & miRNA-155 & 0.1 fM–10 nM & 0.03 fM & [207] \\  & HER2 & 100 pM–1.0 \(\mu\)M & 1.0 pM & [208] \\  & EGFR & 10 fM–10 nM & 10 fM & [209] \\  & CA125 & \(10^{-9}\)–\(1\) U/mL & \(5\times 10^{-10}\) U/mL & [210] \\ EIS & BRCA1 & 50 fM–10 nM & 1.72 fM & [211] \\  & HER2 & 1 pg/mL–100 ng/mL & 172 pg/mL & [212] \\  & miRNA-155 & 10 nM–1.0 nM & 5.7 nM & [213] \\  & miRNA-21 & 10 fM–100 pM & 4.3 fM & [214] \\  & EGFR & 1 pg/mL–1 ug/mL & 0.88 pg/mL & [215] \\  & HER2 & 0–4.0 ug/L & 6.0 ug/L & [216] \\ \hline \end{tabular}
\end{table} 
Table 2: A summary of linear range and limit of detection of different biosensors. Determining different biomarkers in a sample at a specific time is to be considered a primary challenge. In that case, several biosensors can be considered for detecting different biomarkers in the same sample at a specific time. This challenge can be resolved if several techniques are considered to design a complex biosensor that has high sensitivity, specificity, and a simple operation procedure and can simultaneously detect multiple targets. This complex biosensor can be designed under two considerations: (a) the strategy, by which biomarkers are to be detected, should include improving the sensitivity and enhancing the specificity, and (b) the detection equipment should be easy to operate and able to complete multi-target detection simultaneously. For developing a complex biosensor, the mechanism of electrochemical and optical biosensors can be combined with the mechanism of microfluidic chips to achieve better performance. Most of the microfluidic-chip-based biosensors are innovative in devices, while electrochemical and optical biosensors are more innovative in terms of detection strategies and materials.