Abstract
The neural circuits of the infant brain are rapidly established near 6 months of age, but neurodevelopmental disorders can be diagnosed only at the age of 2–3 years using existing diagnostic methods. Early diagnosis is very important to alleviate life-long disability in patients through appropriate early intervention, and it is imperative to develop new diagnostic methods for early detection of neurodevelopmental disorders. We examined the serum level of secretogranin II (SCG2) in pediatric patients to evaluate its potential role as a biomarker for neurodevelopmental disorders. A plasmonic immunosensor performing an enzyme-linked immunosorbent assay (ELISA) on a gold nanodot array was developed to detect SCG2 in small volumes of serum. This nanoplasmonic immunosensor combined with tyramide signal amplification was highly sensitive to detect SCG2 in only 5 μL serum samples. The analysis using the nanoplasmonic immunosensor revealed higher serum SCG2 levels in pediatric patients with developmental delay than in the control group. Overexpression or knockdown of SCG2 in hippocampal neurons significantly attenuated dendritic arborization and synaptic formation. These results suggest that dysregulated SCG2 expression impairs neural development. In conclusion, we developed a highly sensitive nanoplasmonic immunosensor to detect serum SCG2, a candidate biomarker for the early diagnosis of neurodevelopmental disorders.
Highlights
The sandwich enzyme-linked immunosorbent immunoassay (ELISA) was performed under optimized conditions by varying the concentration of SCG2 diluted in 10% human serum to generate a standard curve; the absorbance exhibited linearity (R2 = 0.9911) corresponding to SCG2 concentration
For the detection of SCG2, a candidate serum biomarker of neurodevelopmental disorder, the nanoplasmonic immunosensor employs an enzyme precipitation reaction combined with a tyramide amplification strategy
5 μL of clinical serum sample was not sufficient for conventional ELISA because SCG2 concentration was below its limit of detection (LOD)
Summary
We examined the serum level of SCG2 in pediatric patients using a nanoplasmonic immunosensor to predict its potential role as a biomarker for neurodevelopmental disorders. After the conformation of immunocomplex between antibody and antigen, the enzyme-driven catalytic reaction produces an insoluble precipitate with a high dielectric constant that is stacked on the metal surface This approach increases the effective change in the refractive index near the metal surface and allows for the sensitive detection of molecular events occurring at the surface of metal nanostructures. HRP catalyzes the reporter-conjugated tyramine, and the deposition of active tyramine at the site of the enzyme reaction induces the accumulation of large numbers of reporter molecules that enhance the signal[26,27,28] In this assay, biotin-conjugated tyramide deposited by HRP binds with streptavidin-conjugated alkaline phosphatase (AP), resulting in localized signal enhancement. The enhanced nanoplasmonic immunosensor (E-NPIS) enabled the detection of serum SCG2 in small volumes of samples to evaluate its potential as a biomarker for neurodevelopmental disorders
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