Two nonlinear adaptive versions of the conventional seeker optimization algorithm (SOA) have been proposed for the design of fractional-order controllers using frequency domain specifications. The highly nonlinear and undetermined nature of equations resulting from controller design specifications rules out obtaining a closed-form solution. In this regard, the controller design task has been formulated as an optimization problem and solved using modified variants of the SOA. With the nonlinear adaptation of tuning parameters, the proposed variants of the SOA increase the probability of finding global optima along with improved convergence speed. This has been achieved by incorporating exponential weighting and chaotic behavior in the search process. The validation of the proposed techniques on a set of fractional-order controller design problems clearly exhibits their superiority over other algorithms and controller design techniques. The hardware implementation of the controllers on a DSP TMS320F2812 board ensures applicability for real-time applications.