library(ggplot2)

ic50_val <- 8.1
ic50_sd  <- 0.001

label_text <- paste0(
  'EC[50]=="', sprintf("%.2f", ic50_val),
  '"%+-% "',  sprintf("%.2f", ic50_sd),
  '"*mu*M'
)

ggplot(data.frame(x=1, y=1), aes(x, y)) +
  annotate("text", x = 1, y = 1,
           label = label_text,
           parse = TRUE,
           size = 5)

dir_path <- getwd()

ggsave(filename = paste0(Sys.Date(),"-",".tif"), plot = last_plot(), 
       device = "tiff", path = dir_path,
       scale = 1, width = 9, height = 7, units = "cm",dpi = 300, 
       limitsize = TRUE, compression = "lzw")