Table 2.
Representative examples of recently developed SPR-based optical biosensors for the detection of IL-6.
| Type of Biosensor | Strategy of Detection | LOD | Linear Range | Matrix | Advantages | Disadvantages | Ref. |
|---|---|---|---|---|---|---|---|
| SPR | SPRi array technique and immobilization of antibody or IL-6 inhibitor on the surface of gold chip | 3 pg mL−1 (antibody), 1.1 pg mL−1 (inhibitor) | 3–20 pg mL−1
1.1–20 pg mL−1 |
Plasma | High sensitivity and selectivity, good precision and recovery, rapid incubation time (10 min), label-free assay, real time monitoring | Narrow linear range, the need for spectrophotometer device | [45] |
| LSPR | Microfluidic channel arrays with immobilized gold nanorods conjugated with antibody | 11.29 pg mL−1 | nr * | Serum | Label-free assay, high sensitivity and selectivity, multiplex assay, no cross-reactivity for other cytokines, high accuracy, the need for a small sample volume, label-free assay, real time monitoring | Non determination of linear range, long incubation time (30 min), the need for spectrophotometer device | [47] |
| LSPR | Microfluidic channel arrays with immobilized gold nanorods conjugated with antibody-derived peptide aptamers | 4.6 pg mL−1 | 5 to 1 × 106 pg mL−1 | Serum | High sensitivity and selectivity, label-free assay, the need for a small sample volume, total assay time of 35 min, high consistency with the “gold standard” ELISA, label-free assay, real time monitoring |
The need for spectrophotometer device, low reproducibility in complex biological medium | [48] |
| LSPR | A single-cell secretion detection chip consisting of microwells, each well is surrounded by Au nanopillars capable of LSPR measurement, modification of Au nanopillar with IL-6 antibodies for the direct detection of single-cell secreted IL-6 via LSPR absorbance peak shift | Single-cell cytokine secretion | - | - | High specificity, cost-effective fabrication, label-free assay, real time monitoring | Non-determination of LOD and linear range, the need for spectrophotometer device, non-application | [49] |
| SPR | Direct immobilization of primary antibody through mixed self-assembled monolayer (SAM) using mercaptoundecanoic acid (MUA) and 6-mercapto-1-hexanol (MCH) on a gold surface, and indirect antibody immobilization to the Fc-binding domain of protein G on the mixed SAM; a sandwich complex formation between primary antibody, IL-6 and secondary antibody |
1.3 ng mL−1—Direct 5.7 ng mL−1—Indirect |
0.78–12.5 ng mL−1 | - | High specificity, label-free assay, real time monitoring | Low sensitivity, narrow linear range, not applicable in the real sample, the need for spectrophotometer device, non-application | [50] |
| LSPR | Antibody immobilization on the surface of gold-capped nanopillar-structured cyclo-olefin-polymer (COP) film and observation of peak red-shift in the transmittance spectrum after IL-6 binding |
10 ng mL−1 | - | - | Label-free assay, real time monitoring, high specificity | Low sensitivity, non, determination of linear range, not applicable in the real sample, the need for spectrophotometer device, non-application | [51] |
* nr: not reported.