I am trying to extract information about the nucleotide signal strength at each location for a .ab1 file. Basically I want the ratio of the parameters P1AM and P2AM

library(sangerseqR)
x=read.abif(file.choose())
x$P1AM

This gives me an error saying $ is not an operator for Class S4. Is there a way to achieve what I am trying to do ?

The 'P1AM' and 'P2AM' fields are inside the 'Data' slot - you can find this by using str(x). You can pull out these fields using the @ operator - x@Data$P1AM will do the trick.